Adapting a scan motion in an x-ray imaging apparatus

ABSTRACT

According to one embodiment, the x-ray apparatus comprises an x-ray source adapted to emit an x-ray beam, a detector adapted to receive the x-ray beam of the x-ray source, wherein the x-ray source is adapted to be moved in relation to a first portion of the x-ray apparatus, wherein the detector is adapted to be moved in relation to a first portion of the x-ray apparatus, the x-ray apparatus further comprising a control unit for controlling the movement of the x-ray source and detector, wherein the x-ray source and the detector are adapted to rotate in relation to a first portion of the x-ray apparatus, wherein further the x-ray beam is directed essentially towards the detector during the movement of the x-ray source and the detector.

TECHNICAL FIELD

The present invention relates generally to an x-ray imaging apparatus inthe field of mammography, tomosynthesis and radiography.

BACKGROUND ART

Tomosynthesis is used to reconstruct a three-dimensional image of aperson's body part, for example a breast in a mammography examination.The typical arrangement for creating such images require that the focalspot of an x-ray source (104, 204, 304) is allowed to rotate in relationto an object (108, 208, 308) such as a breast, whereby an interval ofprojection angles through each location in the object (108, 208, 308) isscanned creating individual projection images for each projection angle.With data comprising a multitude of 2D projection images, reconstructioninto a 3D image is possible using computers running algorithms includingback-projection as a computational step. Examples of algorithms arefiltered back projection, algebraic reconstruction and Lange-FesslerConvex algorithm from 1995. Examples x-ray imaging apparatuses enablingthe construction of tomosynthesis images are for instance U.S. Pat. No.7,302,031 and U.S. Pat. No. 6,496,557.

In prior art, x-ray systems with the capability of creating projectionangles, i.e. tomo-angles, has been proposed. Generally, such solutionsallow either a linear or rotational movement of the x-ray source (104,204, 304) in relation to the detector (105, 205, 305) and the object(108, 208, 308) to be scanned, wherein the detector (105, 205, 305) mayalso be adapted to be movable in a linear or rotational manner. It hasbeen proposed to allow for the creation of both 2D images, wherein thex-ray source (104, 204, 304) is stationary and the detector (105, 205,305) rotates around the x-ray source (104, 204, 304) and theinvestigated object, and 3D tomosynthesis images, wherein the x-raysource (104, 204, 304) is movable in relation to the detector (105, 205,305) and the investigated object, in the same system. Examples of suchsystems can for instance be found in U.S. Pat. No. 7,302,031 and U.S.Pat. No. 6,496,557.

X-ray systems as described in the prior art with the capacity togenerate variable tomosynthesis images requires heavier systems andpreferably more complex scan motions with more degrees of freedom thantraditional 2D x-ray imaging systems in order to achieve the soughtafter projection angles and images. However, the scan movement during amammography investigation of such systems is set by an operator based onpreset movement schemes. This will have a negative implication on theimage quality as the most optimal projection angles are not achieved foreach object (108, 208, 308) that is scanned, concerning for instance thesize, thickness and other characteristics of the object. Further, suchsystems does not have the ability to prevent certain scan movements thatshould be avoided based on characteristics of the object that is scannedin a direct or indirect manner.

Further, the solutions in the prior art does not describe an adaptivecontrolling of the scan movement wherein external data is taken intoaccount in order to optimize the tomo-angles during a scan of an object.

In prior art shielding apparatuses used in mammography applications ithas been proposed to use box or telescopic shielding means forprotecting the patient and operator against scatter. Such exemplaryprior art can for instance be seen in EP1480560 B1 which disclosesscanning apparatus wherein the x-ray source is fixed during the scanningmovement. The shielding means herein is automatically installed in avertical direction based upon the installment of the patient breastsupport which height is based on the size of the object to be scanned.The purpose of such solutions are to prevent scattered radiation, not toprevent the direct radiation that does not add to the generation orimprovement of an image of a scanned object.

In prior art it has been proposed to use a position encoder in an x-rayimaging system to synchronize the receiver readout with the scanningmotion so as to yield a high fidelity composite 2D image. Herein theencoders are used to produce signals as a function of detector arraymotion, wherein these signals are used to trigger charge shifting acrossan array of pixels. Since the charge shifting is referenced to encoderoutput, synchronization is maintained despite variances in drive speedor due to other irregularities.

In other prior art documents, tomosynthesis is a method used toreconstruct a three-dimensional image of a person's body part, forexample a breast in a mammography examination. The typical arrangementfor creating such images requires that the focal spot of an x-ray sourceis allowed to move in relation to an object such as a breast, whereby aninterval of projection angles through each location in the object isscanned creating individual projection images for each projection angle.With data comprising a multitude of 2-dimensional projection images,reconstruction into a 3D image is possible using computers runningreconstruction algorithms involving so-called back-projection as acomputational step. Examples of documents disclosing x-ray imagingapparatuses enabling the construction of tomosynthesis images are forinstance U.S. Pat. No. 7,302,031 and U.S. Pat. No. 6,496,557.

Tomosynthesis scanners with variable scan motions require heaviersystems and preferably more complex scan motions with more degrees offreedom than traditional x-ray imaging systems in order to achieve andoptimize the projection angles and images. However, the reconstructionof 3D images requires a precision in the scan motion in order not tocause motion blur in the reconstructed image which is non-compliant tothe heavy systems described in which play is prone to develop over time,for instance in various actuation mechanisms that are used forcontrolling the movement of a certain scan, as well as due to the motorscontrolling the scan motion which are not possible to control in aperfect manner. In order to obtain precise image quality withoutartifacts resembling motion blur, prior art may have to rely onexpensive movement control systems and motors, and force transmissionwithout backlash or deflection.

SUMMARY OF INVENTION

An object of the present invention is to alleviate some of thedisadvantages of the prior art and to provide an improved device for anx-ray imaging system wherein scan motion is optimized based on externaldata.

According to one embodiment, the x-ray apparatus comprises an x-raysource adapted to emit an x-ray beam, a detector adapted to receive thex-ray beam of the x-ray source, wherein the x-ray source is adapted tobe moved in relation to a first portion of the x-ray apparatus, whereinthe detector is adapted to be moved in relation to a first portion ofthe x-ray apparatus, the x-ray apparatus further comprising a controlunit for controlling the movement of the x-ray source and detector,wherein the x-ray source and the detector are adapted to rotate inrelation to a first portion of the x-ray apparatus, wherein further thex-ray beam is directed essentially towards the detector during themovement of the x-ray source and the detector, wherein the control unitis adapted to receive external data, wherein the control unit is furtheradapted to control the movement of the x-ray source and the detectorbased on external data, wherein the x-ray apparatus further comprises atleast one position adjustable compression paddle, and a means fordetermining the position of the at least one compression paddle adaptedto output paddle position data corresponding to the position of the atleast one compression paddle, and wherein the external data, which isreceived by the control unit, comprises paddle position data.

According to another embodiment, the detector is adapted to sensecharacteristics of an x-ray beam in real time during a scan movement,wherein the detector is further adapted to output x-ray beam datacorresponding to characteristics of the x-ray beam, and wherein theexternal data, which is received by the control unit for controlling theremainder of the scan movement of the x-ray source and the detector,comprises x-ray beam data.

According to another embodiment, the detector is adapted to receiveimpinging photons from the x-ray source during a scan movement, thedetector further being adapted to detect an x-ray intensity based on therate of impinging photons, wherein the control unit is further adaptedto receive external data from the detector that a scan of an objectplaced in the x-ray beam is initiated by detecting a lower intensity, asan object to be scanned starts attenuating photons from the x-ray beam.

According to another embodiment, the control unit is adapted to controla scan movement and/or the remainder of a scan movement of the x-raysource and the detector based on the external data, such that atomosynthetic scan movement is performed, wherein tomographic projectionangles of an object placed in the x-ray beam are optimized based on theexternal data.

According to another embodiment, the control unit is adapted to controlthe movement of x-ray source and the detector such that the speed of atleast the x-ray source decreases as the first end of the detector sensesa decreased count rate at least during the scan of the object.

According to another embodiment, a first detected x-ray intensitydecreases the speed of at least the x-ray source to a first velocity, asecond detected x-ray intensity decreases the speed of the x-ray sourceto a second velocity, wherein, if the first detected x-ray intensity islower than the second detected x-ray intensity, the first velocity islower than the second velocity at least during a scan of the object.

According to another embodiment, the control unit is adapted to controlthe speed of the detector such that the velocity of the detector islower than the speed of the x-ray source at least during a scan of anobject.

According to another embodiment, the control unit is adapted to controlthe speed of the x-ray source and the detector such that a ratio betweenthe velocity of the x-ray source and the detector is lower for a lowerlower detected x-ray intensity compared to a higher detected x-rayintensity during a scan of the object and/or compared between twoseparate scan of objects.

According to another embodiment, the control unit is adapted to controlthe speed of the x-ray source and the detector such that the ratio ishigh enough to allow the x-ray source to pass the detector in ahorizontal direction during the movement of the x-ray source and thedetector, wherein the count rate corresponds to the object beingscanned.

According to another embodiment, the control unit is adapted to controlthe speed of at least the x-ray source based on the position of the atleast one compression paddle during a scan of the object such that afirst position of the at least one compression paddle sets the speed ofat least the x-ray source to a first velocity, a second position of theat least one compression paddle sets the speed of at least the x-raysource to a second velocity, wherein, if the first position of the atleast one compression paddle is higher in a vertical direction than thesecond position of the at least one compression paddle, the firstvelocity is lower than the second velocity.

-   -   According to another embodiment, the control unit is adapted to        control the speed of the x-ray source and the detector such that        a ratio between the velocity of the x-ray source and the        detector is lower for a higher position of the compression        paddle compared to a lower position of the compression paddle at        least during a scan of the object.

According to another embodiment, the control unit is adapted to controlthe speed of the x-ray source and the detector such that the ratio ishigh enough to allow the x-ray source to pass the detector in ahorizontal direction at least during a scan of the object.

According to another embodiment, the control unit is adapted to controlthe movement of the x-ray source and the detector such that a straightline between the x-ray source and a centre of the detector in relationto a vertical line essentially extending through a first portion of thex-ray apparatus defines an angle (α) wherein the detector moves beforethe x-ray source towards the object to be scanned, wherein the angle (α)is set during a start of a movement of the x-ray source and the detectoruntil scan of an object is initiated, wherein the angle (α) decreaseswith the position of the at least one compression paddle.

According to another embodiment, the control unit is adapted to controlthe speed of the x-ray source and the detector such that the ratio therebetween is high enough so that the angle (α) has a first value, passes 0degrees and has a second value at the end of the scan of an object,wherein the first and second values essentially maximized underconstraint of avoiding collision with a compression paddle.

According to another embodiment, the control unit is adapted to controlthe angle (α) such that the spread of local tomographic projectionangles remains constant during the entire scan movement.

According to another embodiment, the control unit is adapted to controlthe movement of the x-ray source and the detector such that the angle(α) does not exceed a limit value, wherein the limit value iscontinuously varying with the position of the x-ray source and thepositions of the detector, and furthermore depends on the position andtype of the compression paddle.

According to another embodiment, the limit value of angle (α) depends onthe position of the at least one compression paddle.

According to another embodiment, the apparatus comprises two compressionpaddles, wherein an object can be compressed between said twocompression paddles, wherein the limit value of angle (α) decreases ifthe distance between the compression paddles increases.

According to another embodiment, the x-ray apparatus further comprises ascan arm, wherein the x-ray source is arranged at a first position onthe scan arm and the detector is arranged at a second position on thescan arm.

According to another embodiment, the first position of the scan armcorresponds to a first end of the scan arm and the second position ofthe scan arm corresponds to a second end of the scan arm.

According to another embodiment, the scan arm further comprises amulti-slit collimator arranged between the x-ray source and the detectoron the scan arm, wherein the control unit is adapted to control themovement of the x-ray source and the detector such that a collisionbetween the at least on compression paddle and the collimator isprevented.

According to another embodiment, the control unit is adapted to changedirection of the x-ray source and/or the detector at a first turningpoint for the x-ray source and at a first turning point for the detectorrespectively, wherein the x-ray source either moves in a seconddirection or stops after reaching the first turning point and thedetector either moves in a second direction or stops after reaching thefirst turning point, and wherein the second directions are essentiallyopposite the first directions before reaching the first turning points.

According to another embodiment, the control unit is further adapted toselect the number of turning points, zero or more, and their positionsdepending on said external data.

According to another embodiment, the control unit is further adapted tominimize the number of turning points under the constraint of achievingtomo-angles in the object scan, depending on said external data.

According to another embodiment, the control unit is adapted to controlthe movement of the x-ray source and the detector such that when boththe x-ray source and the detector move towards their first turningpoints the x-ray source reaches the first turning point before thedetector reaches the first turning point.

According to another embodiment, the control unit is adapted to controlthe movement of the x-ray source and the detector such that the x-raysource and the detector changes direction immediately after reaching thefirst turning point and starts to move in a second direction.

According to another embodiment, the control unit is adapted to changedirection of the x-ray source at a second turning point, wherein thecontrol unit is adapted to control the movement of the x-ray source andthe detector such that the x-ray source changes direction and starts tomove in a first direction at the second turning point when the detectorreaches the first turning point.

According to another embodiment, the x-ray stops after reaching thefirst turning point until the other of the x-ray source and detectorreaches the first turning point, whereafter the x-ray source or startsto move in a second direction.

According to another embodiment, the x-ray source moves with a higherspeed than the detector.

According to another embodiment, the control unit is further adapted tocontrol the movement of the x-ray source and the detector based on apositions of the x-ray source and the detector.

According to another embodiment, the positions are predefined.

According to another embodiment, the control unit is adapted to controlthe movement of the x-ray source and the detector such that the speed ofthe x-ray source is higher than the speed of the detector.

According to another embodiment, the predefined positions corresponds topositions reached during a scan of an object, whereby an area in theobject has been identified that requires a specific scan movement,wherein the ratio of the speed of the x-ray source and the detectorincreases.

According to another embodiment, an optimization is performed formaximizing a tomographic angle within a detected object, under atradeoff of minimizing the movement of the X-ray source

According to another embodiment, that the speed of at least the x-raysource decreases as the predefined position of the x-ray source isreached, and the predefined position of the detector is reached.

According to another embodiment, the x-ray apparatus further comprises adevice for taking biopsy samples from a breast as the positions arereached, wherein the positions corresponds to positions whereby an areain the object is identified that requires biopsy sampling.

According to another embodiment, the x-ray apparatus comprises an upperportion and a lower portion, wherein the x-ray source is pivotallyarranged in a first end of a first suspension arm, wherein the secondend of a first suspension arm being slidingly arranged in a first end ofa second suspension arm, wherein a second end of the second suspensionarm is pivotally arranged in a lower portion, wherein a first linearscrew is arranged in the x-ray portion near the x-ray source to controlthe movement of the x-ray source in a horizontal direction, a secondlinear screw is arranged in the lower portion near the detector assemblyto control the movement of the detector assembly in a horizontaldirection, and a third linear screw is arranged in the second suspensionarm to control the movement of the scan arm in a vertical direction.

According to another embodiment, the first portion of the x-rayapparatus is essentially fixed in space.

According to another embodiment, an x-ray apparatus comprises an x-raysource adapted to emit an x-ray beam, a detector adapted to receive thex-ray beam of the x-ray source, wherein the x-ray source is set up to bemoved, wherein the detector is set up to be moved, the x-ray apparatusfurther comprising a control unit for controlling the movement of thex-ray source and detector, wherein further the x-ray beam is directedessentially towards the detector during the movement of the x-ray sourceand the detector, wherein the control unit is adapted receive externaldata, wherein the to control unit is further adapted to control the pathof movement of the combination of the x-ray source and the detectorbased on said external data wherein external data comprises data relatedto an object

According to another embodiment, the control unit is adapted to controlthe movement of the x-ray source along a first movement path and controlthe movement of the detector along a second movement path respectivelyduring a scan movement, based on external data.

According to another embodiment, the external data is received by thecontrol unit during the scan movement.

According to another embodiment, the external data is related to aboundary or thickness of an object to be scanned, or a region ofinterest, wherein said apparatus comprises means for measuring saidexternal data after positioning the object but before finishing a scan.

According to another embodiment, movement of the x-ray source along afirst movement path and the movement of the detector along the secondmovement path, corresponds to a combined movement path, wherein saidcombined movement path can be represented by a curve through amulti-dimensional parametric space involving a position along one axisand an angle between said x-ray source and detector.

According to another embodiment, said first movement path and saidsecond movement path is adapted for optimizing local tomographicprojection angles and minimizing movements of said x-ray source.

An object of the present invention is to alleviate some of thedisadvantages of the prior art and to provide an improved device forshielding x-ray radiation.

According to one embodiment, the x-ray apparatus comprises an x-raysource adapted to emit an x-ray beam, a detector adapted to receive thex-ray beam of the x-ray source, wherein the x-ray source is adapted tobe moved in relation to a first portion of the x-ray apparatus, whereinthe detector is adapted to be moved in relation to the first portion ofthe x-ray apparatus, wherein the x-ray source and the detector areadapted to rotate in relation to the first portion of the x-rayapparatus, wherein further the x-ray beam is directed essentiallytowards the detector during the movement of the x-ray source and thedetector, the x-ray apparatus further comprising; a position sensingarrangement adapted for sensing positions corresponding to the positionsof the x-ray source and the detector and transmitting the positionsignals corresponding to the positions of the x-ray source and thedetector as sensed by the position sensing arrangement, a field limitingdevice, comprising a first side portion and a second side portion and anopening between the side portions, wherein the x-ray beam is allowed topass through the opening but is blocked by the first and second sideportions wherein it is absorbed by the first and second side portions,

According to another embodiment, at least the first side portion of thefield limiting device is adjustably movable in relation to a center lineof the x-ray beam, between a first position and second position whereinthe first side portion prevents a larger share of the x-ray beam frompassing the field limiting device in the second position than in thefirst position, wherein the apparatus further comprises a first controlunit adapted for receiving the position signals from the positionsensing arrangement and wherein the first control unit is adapted tocontrol the movement of at least the first side portion based on theposition signals.

According to another embodiment, the first side portion prevents alarger share of the x-ray radiation from passing the field limitingdevice in any position between the first position and the secondposition compared to the first position.

According to another embodiment, the second position of the first sideportion is closer to a center of the x-ray beam than the first positionof the first side portion.

According to another embodiment, the x-ray apparatus further comprisesan image field having at least a first end and a second end, wherein thefirst side portion is adapted to move towards a second position toprevent x-ray radiation from irradiating an area outside the first imageend, and the second side portion is adapted to move towards a secondposition to prevent x-ray radiation from irradiating an area outside thesecond image end.

According to another embodiment, the x-ray apparatus further comprises ascan arm, wherein the x-ray source is arranged on a first position of ascan arm, wherein the detector is arranged on a second position of thescan arm, wherein the field limiting device is arranged on a thirdposition of the scan arm, such that a movement of the x-ray sourcecauses a movement of the field limiting device.

According to another embodiment, an opening of the field limiting devicecomprises a first angle v_(f1) from the center line of the x-ray beam tothe end of the first side portion seen from the x-ray source, a secondangle v_(f2) from a center line of the x-ray beam to the end of thesecond side portion seen from the x-ray source wherein v_(i2) is theangle from a center line of the x-ray beam to the second image end seenfrom the x-ray source, wherein v_(i1) is the angle from a center line ofthe x-ray beam to the first image end seen from the x-ray source,wherein v_(d2) is the angle from a center line of the x-ray beam to asecond end of the detector seen from the x-ray source, wherein v_(d1) isthe angle from a center line of the x-ray beam to a first end of thedetector seen from the x-ray source, wherein the first side portion isadapted to move between a first and second position if v_(i1)<v_(d1),such that v_(f1)≦v_(i1), wherein the second side portion is adapted tomove between a first and second position if v_(i2)<v_(d2) such thatv_(f2)≦v_(i2)

According to another embodiment, the first side portion is adapted tomove between a first and second position if v_(i1)>v_(d1), such thatv_(d1)≦v_(f1)≦v_(i1) wherein the second side portion is adapted to movebetween a first and second position if v_(i2)>v_(d2), such thatv_(d2)≦v_(f2)≦v_(i2).

According to another embodiment, the first side portion moves towardsthe second position if v_(i1) is decreasing and moves towards the firstposition if v_(i1) is increasing, and the second side portion movestowards the second position if v_(i2) is decreasing and moves towardsthe first position if v_(i2) is increasing.

According to another embodiment, wherein the x-ray apparatus is setup toperform plural scan sweeps, the x-ray apparatus further comprises asecond control unit for controlling the movement of the x-ray source andthe detector, wherein the detector comprises a plurality of detectorlines, wherein the first control unit is adapted to calculate the anglesof the x-ray beam towards each of the detector lines in relation to avertical line at predefined positions along a path essentially extendingin a horizontal direction, based on the position signals from theposition sensing arrangement, wherein first control unit is adapted tosave the calculated angles wherein the first control unit is adapted tocontrol at least the first side portion of the field limiting device toprevent the x-ray beam from being received by the detector lines morethan once for each calculated angle at each predefined position alongthe path essentially extending in a horizontal direction.

According to another embodiment, the second control unit is adapted tochange direction of the x-ray source and/or the detector at a firstturning point of the x-ray source and a first turning point of thedetector respectively, wherein the x-ray source and the detector, afterreaching the turning point, move in a second direction which isessentially opposite a first direction prior to reaching the turningpoint, wherein a main scan movement comprises the movement of the x-raysource and the detector before the x-ray source reaches the firstturning point and after the detector reaches the first turning point,wherein a bouncing scan movement comprises the movement of the x-raysource and the detector from when r the x-ray source reaches the firstturning point until the detector reaches the same turning point or fromwhen the x-ray source reaches the first turning point, the detectorreaches the first turning point, and until the x-ray source reaches asecond turning point wherein the x-ray source changes direction ofmovement again, wherein the first control unit is adapted to compare thesaved calculated angles during a main scan movement with the calculatedangles during a bouncing scan movement, and wherein the first controlunit is further adapted to identify and mark the detector lines forwhich there is an overlap during a main scan and a bouncing scanmovement wherein first control unit is adapted to move at least thefirst side portion towards a second position such that at least thefirst side portion will essentially cover the marked detector lines fromthe x-ray beam.

According to another embodiment, the first and second side portions areinterconnected with each other.

According to another embodiment, the field limiting device comprises aplate with an aperture.

According to another embodiment, the field limiting device comprises acylindrical device having an aperture, wherein the portion of thecylindrical device defining a first end of the aperture is the firstside portion, and the portion of the cylindrical device defining asecond end of the aperture is the second side portion, wherein thecylindrical device is pivotally arranged for rotation around the x-raysource.

According to another embodiment, the cylindrical device is adapted torotate an angle v_(rot1)=(v_(f1)−v_(i1)), if v_(i1)<v_(f1), and whereinthe cylindrical device is adapted to rotate an anglev_(rot2)=(v_(f2)−v_(i2)), if v_(i2)<v_(f2).

According to another embodiment, the cylindrical device is adapted torotate an angle v_(rot1)=(v_(f1)−v_(d1)), if v_(i1)>v_(d1) and rotate anangle v_(rot2)=(v_(f2)−v_(d2)), if v_(i2)>v_(d2).

According to another embodiment, a second side portion is adapted tomove towards a first position, a second position or not move, as thefirst side portion moves towards the second position, wherein the secondside portion prevents a larger share of the x-ray beam from passing thefield limiting device in a second position than in a first position.

According to another embodiment, the second position of the second sideportion is closer to a center line of the field than the first positionof the second side portion.

According to another embodiment, the movement of the first and secondside portions is performed by an electrical motor, wherein the motor iscontrolled by the first control unit.

According to another embodiment, the first side portion and second sideportion are adapted to slide along at least one linear rail.

According to another embodiment, the first and second side portions areL-shaped.

According to another embodiment, the first side portion and second sideportion are made of an x-ray opaque material such as steel and/or lead.

According to another embodiment, the first control unit is adapted tocontrol the movement of a first and second side portion based on themovement of the x-ray source and the movement of the detector.

According to another embodiment, the first control unit is adapted tocontrol the movement of the first and second side portions based on atleast one preset scan program.

According to another embodiment, the first position of the scan armcorresponds to a first end of the scan arm, and wherein a secondposition of the scan arm corresponds to a second end of the scan arm.

According to another embodiment, the first and second control unit iscomprised by the same control unit

According to another embodiment, the path essentially extending in ahorizontal direction is located within the distance from an object tableto a compression paddle.

According to another embodiment, the first portion of the x-rayapparatus is essentially fixed in space.

According to another embodiment, the x-ray apparatus comprises; an x-raysource (104, 204, 304) adapted to emit an x-ray beam; a detector adaptedto receive the x-ray beam of the x-ray source, wherein the x-ray source(104, 204, 304) is adapted to be moved, wherein the detector is adaptedto be moved, wherein further the x-ray beam is directed essentiallytowards the detector during the movement of the x-ray source (104, 204,304) and the detector, wherein at least the first side portion (140 a,240 a, 340 a) of the field limiting device (140, 240, 340) is adjustablymovable in relation to a center line of the x-ray beam between a firstposition and second position, wherein the first side portion (140 a, 240a, 340 a) prevents a larger share of the x-ray beam from passing thefield limiting device (140, 240, 340) in the second position than in thefirst position, wherein the movement of the x-ray source (104, 204, 304)and the detector (105, 205, 305) is synchronized with the movement ofthe field limiting device (140, 240, 340). With the synchronization, anysolution comprising a predefined relationship between the movement ofthe field limiting device and the movement of the x-ray source and thedetector, for instance, the use of predefined movement paths performedat a given time, and during a certain time frame, wherein positions ofthe x-ray source and the detector are reached at certain points in time,or the use of a stepper motor(s) for driving the movement of the x-raysource and detector.

According to another embodiment, an x-ray apparatus for tomosynthesisimaging comprises an X-ray source, an indicated area for exposure, adetector and a field limiter for controlling an extent of an X-ray beam,

a controller for moving in synchronism said field limiter, and saidX-ray source during exposure from said X-ray source,said controller being adapted for limiting an edge of said X-ray beam toan edge of said area of exposure.

An object of the present invention is to alleviate some of thedisadvantages of the prior art and to provide an improved device forx-ray imaging wherein motion blur in an image reconstruction can bereduced at a low cost.

According to one embodiment, the x-ray apparatus comprises an x-raysource adapted to emit x-ray beams, a detector adapted to receive thex-ray beams emitted by the x-ray source, wherein the x-ray source isarranged to be moved in relation to a first portion of the x-rayapparatus, wherein the detector is arranged to be moved in relation tothe first portion of the x-ray apparatus, the x-ray apparatus furthercomprising a control unit for controlling the movement of the x-raysource and the detector, wherein the x-ray source and the detector areadapted to move in relation to the first portion of the x-ray apparatus,wherein further the x-ray beams are directed essentially towards thedetector during the movement of the x-ray source and the detector,wherein data concerning the x-ray beams is read out during the movementof the x-ray source and the detector. According to another embodiment,the x-ray apparatus further comprises a position sensing arrangementadapted for sensing positions corresponding to the positions of thex-ray source and the detector and transmitting the position signals, arecording device adapted to receive and record the position signalscorresponding to the positions of the x-ray source and the detector assensed by the position sensing arrangement, an image reconstructiondevice connected to the detector via a first connection device, andconnected to the recording device via a second connection device,wherein the image reconstruction device is adapted for reconstructing animage based on the recorded positions in the recording device and theread out data from the detector. By including the actual positions ofthe x-ray source and the detector in the tomosynthesis reconstructionprocess, the detector readout images can be optimized in terms ofreduced motion blur effects.

According to another embodiment, the x-ray apparatus further comprises ascan arm wherein the x-ray source is arranged at a first position of thescan arm and the detector is arranged at a second position of the scanarm.

According to another embodiment, the scan arm is pivotally arranged in asecond portion of the x-ray apparatus.

According to another embodiment, the second portion of the x-rayapparatus comprises a first suspension arm wherein the first suspensionarm comprises a first and second end and the first end of the scan armis pivotally arranged in the first end of the first suspension arm.

According to another embodiment, a second end of the first suspensionarm is adapted to be linearly displaceable in relation to a first end ofa second suspension arm, such that a total length of the first andsecond suspension arms can be varied.

According to another embodiment, either the second end of the firstsuspension arm is arranged inside the first end of the second suspensionarm or the first end of the second suspension arm is arranged inside thesecond end of the first suspension arm, wherein the first and secondsuspension arms have a telescopic relationship.

According to another embodiment, the second end of the second suspensionarm is pivotally arranged in a lower portion of the x-ray apparatus.

According to another embodiment, the position sensing arrangementcomprises a first position sensing device adapted to sense a relativerotational movement between the scan arm and the second portion of thex-ray apparatus.

According to another embodiment, the first position sensing devicecomprises a first rotary position encoder arranged essentially where thefirst end of the scan arm is pivotally arranged in a first end of thefirst suspension arm.

According to another embodiment, the position sensing arrangementcomprises a second position sensing device adapted to sense a relativerotational movement between the second suspension arm and the lowerportion of the x-ray apparatus, wherein the second position sensingdevice comprises a second rotary position encoder.

According to another embodiment, the position sensing arrangementfurther comprises a third position sensing device adapted to sense thelinear displacement between the second end of the first suspension armand the first end of the second suspension arm.

According to another embodiment, the third position sensing devicecomprises a position scale arranged either at the second end of thefirst arm or the first end of the second arm and that the secondposition sensing device further comprises a position sensor arranged onthe other of the second end of the first arm or the first end of thesecond arm.

According to another embodiment, the x-ray apparatus further comprises afirst motor for controlling the rotational movement of the scan arm inrelation to a second portion of the x-ray apparatus, wherein theposition sensing arrangement comprises a fourth position sensing deviceadapted to sense the relative rotational position of a casing of thefirst motor and the rotor of the first motor, wherein the set relativerotational position of the scan arm and the second portion is sensed.

According to another embodiment, the x-ray apparatus further comprises asecond motor for controlling the rotational movement of the secondportion in relation to the lower portion of the x-ray apparatus, whereinthe position sensing arrangement further comprises a fifth positionsensing device, adapted to sense the relative rotational position of acasing of the second motor and the rotor of the second motor, whereinthe set relative rotational position of the second portion and the lowerportion is sensed.

According to another embodiment, the x-ray apparatus further comprises athird motor for controlling the linear displacement of the first end ofthe first suspension arm in relation to second end of the secondsuspension arm, wherein in the position sensing arrangement furthercomprises a sixth position sensing device, adapted to sense the relativerotational position of a casing of the third motor and the rotor of thethird motor, whereby the set relative linear displacement of the firstend of the first suspension arm in relation to second end of the secondsuspension arm can be deduced.

According to another embodiment, an alteration of the signals isperformed in the image reconstruction device before the reconstructionof an image.

According to another embodiment, the position sensing arrangement isconnected to the recording device via a third connection device fortransmitting the signals to the recording device, wherein the first,second and third connection devices are one of a signal cable or atransmitter for wireless communication.

According to another embodiment, readout of data is performed upon theposition signals from at least one of the fourth, fifth and sixthposition sensing devices, corresponding to predefined positions.

According to another embodiment, readout of data is performed at certainpredefined points in time.

According to another embodiment, readout of data is performed uponposition signals from the position sensing arrangement, corresponding topredefined positions.

According to another embodiment, comprising a method for imagereconstruction, the x-ray apparatus comprising an x-ray source and adetector, wherein the x-ray source is adapted to emit x-ray beams,wherein the detector is adapted to receive the emitted x-ray beams, themethod including the steps: moving the x-ray source and detector in alinear and/or rotational manner during a scan movement, recording themovement in space of the scan arm at certain predefined positions or atcertain points in time, reconstructing an x-ray image based on therecorded movement of the scan arm and the received x-ray radiation.

According to another embodiment, comprising a method for imagereconstruction, the movement of the scan arm in space is recorded byrecording relative positions of portions of the x-ray apparatus.

According to another embodiment, the x-ray apparatus further comprises adisplay device adapted to display the generated images, reconstructed bythe image reconstruction device.

According to another embodiment, the first portion of the x-rayapparatus is essentially fixed in space.

According to another embodiment, the x-ray source is adapted to be movedin relation to the first portion of the x-ray apparatus along a firstmovement path, wherein the detector is adapted to be moved in relationto the first portion of the x-ray source along a second movement path,wherein the position sensing arrangement is adapted for sensing thepositions of the x-ray source and the detector along the first andsecond movement paths, respectively.

According to another embodiment, the detector readout and positionsensor readouts are performed in synchronism, and said imagereconstruction involves adapting coordinates for reconstructed voxels orpixels in the projection image data.

According to another embodiment, the apparatus further comprising ameans for synchronization and cross reference of recorded position dataand data from said detector, and said means for reconstruction comprisesa means for computing coordinates for correspondence between detectordata and voxel data.

According to another embodiment, the means for synchronization involvesrecording timing data corresponding to readouts from detector and/or aposition sensor.

According to another embodiment, a scanning apparatus comprising:

scanning mechanics moving with plural degrees of freedomplural position sensors, and a means for recording positions,and an x-ray detector and a means for recording detector readout whilescanning,whereby obtaining a set of projection image data,a reconstruction means for reconstructing an image volumewherein said reconstruction means is characterized by adaptingcoordinates using recorded positions.

BRIEF DESCRIPTION OF DRAWINGS

The invention is now described, by way of example, with reference to theaccompanying drawings, in which:

FIG. 1 illustrates a schematic view of an x-ray imaging system

FIG. 2 shows a schematic view of the x-ray apparatus wherein thearrangement and parts of the apparatus are explained

FIG. 3 shows an example of a possible position of the scan arm

FIG. 4 a shows an embodiment of the invention comprising a positionadjustable compression paddle

FIG. 4 b shows the compression paddle having a position higher than thatof FIG. 4 a

FIG. 5 a-5 b shows an embodiment, wherein the position of thecompression paddle comprises external data

FIG. 6 a-6 b shows an embodiment, similar to that of FIG. 5 a-5 bwherein a collimator is arranged on the scan arm

FIG. 7 a-7 b shows scan movements wherein an angle α is defined

FIG. 8 a-8 b, shows an embodiment wherein external data comprises datafrom the detector

FIG. 9 describes a scan movement around an identified interesting areain an object

FIG. 10 a-10 d illustrates a schematic view of the scan arm at certainpositions of the scan arm during scan movement at a turning point

FIG. 10 e shows the achieved local tomographic projection angles duringthe scan movement according to FIG. 10 a-10 d

FIG. 11 a-FIG. 11 d represents a similar scan movement to that describedin FIG. 10 a-10 d,

FIG. 12 a-12 f illustrates a schematic view of the scan arm at certainpositions of the scan arm during scan movement at a turning point

FIG. 12 g shows the achieved tomo-angles during the scan movementaccording to FIG. 12 a-12 f

FIG. 13 shows an alternative scan movement, wherein the tomo-angle isslightly smaller compared to in FIG. 12 g

FIG. 14 a-FIG. 14 f represents a similar scan movement to that describedin FIG. 12 a-12 f

FIG. 15 a-15 e illustrates a schematic view of the scan arm at certainpositions along a scan movement

FIG. 16 a-16 e represents a similar scan movement to that described inFIG. 15 a-15 f

FIG. 17 shows the scan arm with a field limiting device according to oneembodiment.

FIG. 18 a shows the scan arm with a field limiting device according to aone embodiment wherein a first portion of the field limiting deviceprevents radiation outside a first image end.

FIG. 18 b shows the scan arm with a field limiting device according toone embodiment wherein the field limiting device prevents radiationoutside a second image end.

FIG. 18 c shows the scan arm with a field limiting device according toone embodiment wherein the field limiting device prevents radiationoutside a first end of the detector.

FIG. 18 d shows the scan arm with a field limiting device according toone embodiment wherein the field limiting device prevents radiationoutside a second end of the detector.

FIG. 19 a shows the scan arm with a field limiting device according toanother embodiment in a first position wherein the detector is outsidethe image field.

FIG. 19 b shows the scan arm with a field limiting device according toanother embodiment in a second position wherein the detector is outsidethe image field.

FIG. 19 c shows the scan arm with a field limiting device according toanother embodiment in a first position wherein the detector is insidethe image field.

FIG. 19 d shows the scan arm with a field limiting device according toanother embodiment in a second position wherein the detector is insidethe image field.

FIG. 20 illustrates a schematic view of an x-ray imaging system

FIG. 21 shows a schematic view of the relationship between the first andsecond suspension arms

FIG. 22 shows a schematic view of a side view of the x-ray apparatus

DESCRIPTION OF EMBODIMENTS

In the following, a detailed description of the invention is presented.

FIG. 1 illustrates an x-ray imaging system (101, 201, 301) schematicallyaccording to one embodiment, wherein the system comprising an x-rayapparatus (102, 202, 302). The x-ray apparatus (102, 202, 302) furthercomprising a scan arm (103, 203, 303), wherein an x-ray source (104,204, 304) is arranged on one upper portion (112, 212, 312) of the scanarm (103, 203, 303) but may be arranged at any position along the scanarm (103, 203, 303) according to other embodiments of the invention. Adetector (105, 205, 305) is arranged in the other, lower end of the scanarm (103, 203, 303), the detector (105, 205, 305) comprising a pluralityof detectors strips (105 a, 205 a, 305 a). The detector (105, 205, 305)may however be arranged at any position along a scan arm (103, 203, 303)according to other embodiments of the invention. A collimator (106, 206,306) comprising a plurality of slits (106 a, 206 a, 306 a) is arrangedbetween the x-ray source (104, 204, 304) and the detector (105, 205,305) on the scan arm (103, 203, 303). In an arrangement, separate fromthe scan arm (103, 203, 303) and any motion thereof, the x-ray apparatus(102, 202, 302) further comprises at least one position adjustablecompression paddle (107 a, 107 b; 207 a, 207 b; 307 a, 307 b) forcompressing and fixating an object (108, 208, 308), such as a breast,during a scan.

FIG. 2 shows a schematic view of the x-ray apparatus (102, 103),according to one embodiment, wherein the arrangement and parts of theapparatus that enables both 2D scan motions and 3D scan motions arefurther explained. As seen in the figure, the x-ray source (104, 204,304) is pivotally arranged in a first end of a first suspension arm(109, 209, 309). The first end (109 a, 209 a, 309 a) of the firstsuspension arm (109, 209, 309) may be pivotally arranged in a an upperportion (112, 212, 312) of the x-ray apparatus. The second end (109 b,209 b, 309 b) of the first suspension arm (109, 209, 309) is arrangedlinearly displaceable in relation to a first end (110 a, 210 a, 310 a)of a second suspension arm (110, 210, 310), in a manner such that thetotal length of the first (109, 209, 309) and second suspension arm(110, 210, 310) may be varied. According to one embodiment, the firstsuspension arm (109, 209, 309) is arranged partly inside the secondsuspension arm (110, 210, 310), however the arrangement may be the otherway around, i.e. wherein the second suspension arm (110, 210, 310) ispartly arranged inside the first suspension arm (109, 209, 309).Further, the second end (110 b, 210 b, 310 b) of the second suspensionarm (110, 210, 310) is pivotally arranged in a lower portion (111, 211,311).

In order to control a movement of the x-ray source (104, 204, 304) in ahorizontal direction, a first linear screw (not shown) may be isarranged in x-ray apparatus (102, 202, 302) and connected in one end tothe upper portion (112, 212, 312) near the x-ray source (104, 204, 304).A corresponding second linear screw (not shown) may be arranged in thelower portion (112, 212, 312) and connected to the detector (105, 205,305) to control the movement of the detector (105, 205, 305) in ahorizontal direction. A third linear screw (not shown) may be arrangedin first and/or second suspension arm (110, 210, 310) in order tocontrol the total length of the first and second suspension arm (110,210, 310). Any suitable type of actuation mechanism may however be usedthat enables the horizontal movements between the parts described. Theactuation mechanism may for instance comprise motors driving of varioussize arranged at various positions on the x-ray apparatus. Suchactuation mechanisms is seen schematically in FIG. 1, and is alsofurther explained in connection to FIG. 20, FIG. 21 and FIG. 22.

In order to control the rotational movement of the scan arm (103, 203,303) in relation to the first suspension arm (109, 209, 309), a firstmotor (116, 216, 316), preferably of electrical kind, is arranged,preferably on the first suspension arm (109, 209, 309), wherein a firstsprocket (117, 217, 317) is adapted to be rotated upon the activation ofthe first motor (116, 216, 316) in one of two rotational directions. Asecond sprocket (118, 218, 318), preferably larger than the firstsprocket (117, 217, 317), is arranged on the scan arm (103, 203, 303) inorder to be engaged with the first sprocket (117, 217, 317), wherein arotational movement of the first sprocket (117, 217, 317) is transferredto the second sprocket (118, 218, 318) and to the scan arm (103, 203,303). A second motor (126, 226, 326), preferably an electrical motor andsimilar to the first motor (116, 216, 316), is arranged in the lowerportion (111, 211, 311) or in another part of the x-ray apparatus (102,103), wherein a third sprocket (120, 220, 320) is arranged to be rotatedupon the activation of the motor in one of two rotational directions. Afourth sprocket (120, 220, 320), preferably larger than the thirdsprocket (119, 219, 319) is arranged on the second suspension arm (110,210, 310) in order to be engaged with the third sprocket (119, 219,319), wherein a rotational movement of the third sprocket (119, 219,319) is transferred to the fourth sprocket (120, 220, 320) and to thesecond suspension arm (110, 210, 310). A control unit (121, 221, 321) isconnected to the motors (116, 216, 316, 119, 219, 319) in order tocontrol the motors and thereby the rotational movement of thefirst/second suspension arm (110, 210, 310), and the scan arm (103, 203,303). By the aid of this arrangement, the arbitrary movement in twodimensions of the x-ray source (104, 204, 304) and the detector (105,205, 305) is enabled within the mechanical restraints of the rotationallimits between the scan arm (103, 203, 303) and the first suspension arm(109, 209, 309), the varying of the total length of the first and secondsuspension arm (110, 210, 310), and the connection between the x-raysource (104, 204, 304) and the detector (105, 205, 305) through the scanarm (103, 203, 303). In the embodiment wherein a scan arm (103, 203,303) is not present, an additional degree of freedom in the relativemovement between the x-ray source (104, 204, 304) and the detector (105,205, 305) is present. When the detector (105, 205, 305) and x-ray source(104, 204, 304) are connected by a scan arm (103, 203, 303), an x-raybeam (122, 222, 322) irradiated or emitted from the x-ray source (104,204, 304) is thus set to be directed towards, i.e. aligned with andirradiate or emit, the detector (105, 205, 305). In any embodimentwherein no scan arm (103, 203, 303) is present, and the absolutedistance between the x-ray source (104, 204, 304) and the detector (105,205, 305) may vary, a control unit (121, 221, 321) is adapted to rotatethe x-ray source (104, 204, 304) and the detector (105, 205, 305) suchthat x-ray beams emitted from the x-ray source (104, 204, 304) isadapted to be directed towards, and irradiate the detector (105, 205,305). The words “irradiate” and “emit” is used interchangeablythroughout the application.

During the scan movement of the x-ray source (104, 204, 304) and thedetector (105, 205, 305) in relation to an object, the x-ray source(104, 204, 304) may thus be moved along a thought, arbitrary firstmovement path that may be redefined at any instant in time and betweendifferent scans as well as being rotated during this movement. In asimilar manner, the detector (105, 205, 305) may be moved along athought, arbitrary second movement path that may be redefined at anyinstant in time and between different scans, as well as being rotatedduring this movement. Further, throughout this application, a scanmovement will be referred to as the movement of the x-ray source (104,204, 304) and/or the detector (105, 205, 305) assembly along a first anda second movement path. The scan movement further comprises a subsetwhen the irradiated x-rays are actually impinging on an object (108,208, 308) wherein an image of the objected can be reconstructed. Suchmovements are hereinafter referred to as a scan of an object, oralternatively, object scan. A scan movement may comprise movements ofthe x-ray source and detector necessary for reconstruction of an imagevolume, i.e. tomosynthetic images or at least a slice of an image volumeof the object. Such scan movement requires a scan movement comprisingvarious projection angles through the same point in an object, so calledtomo-angles, or tomographic angles or tomographic projection angles, andtheir spread is often referred to as tomographic angle, which is relatedto vertical resolution. These angles may vary across the image field,whereby the acquired 3d image may have local variations incharacteristics. According to one embodiment, scan movement furthercomprises that the x-ray source emits an x-ray beam towards the detectorwith the purpose of generating x-ray images.

In FIG. 3, an example of a possible position of the scan arm (103, 203,303), and thus the relation of the x-ray source (104, 204, 304) inrelation to the detector (105, 205, 305) is shown, by the aid of thearrangement described above, controlling the movement of the x-raysource (104, 204, 304) and the detector (105, 205, 305). The first andsecond linear screws (not shown), have moved the detector (105, 205,305) as well as the x-ray source (104, 204, 304) portion to the right inFIG. 3. Further, the actuation of the third linear screw (115, 215, 315)has increased the total length of the first and second suspension arm(110, 210, 310), wherein the x-ray source (104, 204, 304) has moved to aposition upwards and to the right in the figure. Naturally, the samemovement may be achieved by the actuation of sprockets 1-4 incombination with the linear screw of the first and second suspension arm(110, 210, 310).

FIG. 4 a shows an embodiment of the invention comprising a positionadjustable compression paddle (107 a, 107 b; 207 a, 207 b; 307 a, 307 b)and a means for measuring the position (123, 223, 323), preferably theheight position, of the compression paddle (107 a, 107 b; 207 a, 207 b;307 a, 307 b) in relation to a fixed point in space. The means formeasuring the position (123, 223, 323) of the compression paddle (107 a,107 b; 207 a, 207 b; 307 a, 307 b) is connected to the control unit(121, 221, 321) for controlling the movement of the x-ray source (104,204, 304) and the detector (105, 205, 305), for instance via a cable(124, 224, 324) or via wireless transmission. The means for measuringthe position (123, 223, 323) of the compression paddle (107 a, 107 b;207 a, 207 b; 307 a, 307 b) is adapted to output data corresponding tothe position of the compression paddle (107 a, 107 b; 207 a, 207 b; 307a, 307 b) to the control unit (121, 221, 321). The control unit (121,221, 321) is adapted to receive such data, also referred to as externaldata throughout this application, wherein the control unit (121, 221,321) is adapted to control the movement of the x-ray source (104, 204,304) and the detector (105, 205, 305) based on this external data.

One example of how the control unit (121, 221, 321) controls themovement of the x-ray source (104, 204, 304) can be seen in the exampleof FIG. 4 a and FIG. 4 b. According to the embodiment of FIG. 4 a, ascan of an object (108, 208, 308) is initiated wherein at least thex-ray source (104, 204, 304) travels with a speed v defined by thecontrol unit (121, 221, 321) based on the position of the compressionpaddle (107 a, 107 b; 207 a, 207 b; 307 a, 307 b). In FIG. 4 b, thecompression paddle (107 a, 107 b; 207 a, 207 b; 307 a, 307 b) has aposition higher than that of 4 b wherein the control unit (121, 221,321) sets a lower speed of at least the x-ray source (104, 204, 304)during the scan. Hence, the control unit (121, 221, 321) is adapted toset a lower speed of the x-ray source (104, 204, 304) if the compressionpaddle (107 a, 107 b; 207 a, 207 b; 307 a, 307 b) is relatively highcompared to another lower position of the compression paddle.

According to one embodiment, if the x-ray source (104, 204, 304) and thedetector (105, 205, 305) moves with respective speeds along their firstand second movement paths, the control unit (121, 221, 321) is adaptedto control the speed of the x-ray source (104, 204, 304) such that theratio between the speed of the x-ray source (104, 204, 304) and thedetector (105, 205, 305) is high enough to allow the x-ray source (104,204, 304) to pass the detector (105, 205, 305) in horizontal directionat least during the scan of an object.

In FIG. 5 a and FIG. 5 b a further aspect of the invention is shown. Thecontrol unit (121, 221, 321) is adapted to control the movement of thex-ray source (104, 204, 304) and the detector (105, 205, 305) based oninput from external data comprising the position of at least onecompression paddle (107 a, 107 b; 207 a, 207 b; 307 a, 307 b) such thata collision between the detector (105, 205, 305) and the compressionpaddle (107 a, 107 b; 207 a, 207 b; 307 a, 307 b) is prevented. Hence, acollision is avoided when the second movement path is not crossing theposition of the compression paddle (107 a, 107 b; 207 a, 207 b; 307 a,307 b), i.e. when the compression paddle (107 a, 107 b; 207 a, 207 b;307 a, 307 b) is outside the second movement path. In FIG. 5 a a portionof the first and second movement paths are shown, wherein the lowercompression paddle (107 a, 107 b; 207 a, 207 b; 307 a, 307 b) is outsidethe second movement path and a collision is avoided. FIG. 5 b, to thecontrary, shows an un-allowed control of the movements of the x-raysource (104, 204, 304) and the detector (105, 205, 305) wherein thecompression paddle (107 a, 107 b; 207 a, 207 b; 307 a, 307 b) is in theway of the second movement path and a collision will eventually occur.

FIG. 6 a and FIG. 6 b show an analogous set up as in FIGS. 5 a and 5 bwith the slight difference of the addition of a collimator (106,206,206). The control unit (121, 221, 321) is adapted to control themovement of the x-ray source (104, 204, 304) and the detector (105, 205,305) based on the input from external data comprising the position of atleast one compression paddle (107 a, 107 b; 207 a, 207 b; 307 a, 307 b)such that a collision between the collimator (106, 206, 306) and thecompression paddle (107 a, 107 b; 207 a, 207 b; 307 a, 307 b) isavoided. In analogy to the defined movement paths of the x-ray source(104, 204, 304) and the detector (105, 205, 305), the collimator (106,206, 306) will move along a third movement path being defined by thefirst and second movement paths. Hence, collision is avoided when thethird movement path is not crossing the position of the compressionpaddle (107 a, 107 b; 207 a, 207 b; 307 a, 307 b), i.e. when thecompression paddle (107 a, 107 b; 207 a, 207 b; 307 a, 307 b) is outsidethe third movement path. In FIG. 6 a a portion of the first, second andthird movement paths are shown, wherein the compression paddle (107 a,107 b; 207 a, 207 b; 307 a, 307 b) is outside the third movement pathand a collision is avoided. FIG. 6 b, to the contrary, shows anun-allowed control of the movements of the x-ray source (104, 204, 304)and the detector (105, 205, 305) wherein the upper compression paddle(107 b, 207, 307 b) is in the way of the third movement path and acollision will eventually occur.

In FIG. 7 a, another type of scan movement possible with the x-rayapparatus (102, 202, 302) according to this invention is shown. Herein,an angle α of the scan arm (103, 203, 303) in relation to a verticalline, is essentially unchanged during the entire scan movement. Theangle α is set during the start of the scan movement by the control unit(121, 221, 321) taking the height position of the compression paddle(107 a, 107 b; 207 a, 207 b; 307 a, 307 b) into consideration, whereinthe angle α of the is roughly inversely proportional to said heightposition, depending on shape of the paddle and patient support. As canbe seen in FIG. 7 b, the angle α of the scan arm (103, 203, 303) is setsmaller for a scan movement by the control unit (121, 221, 321) when thelatter senses a high position of the compression paddle (107 a, 107 b;207 a, 207 b; 307 a, 307 b). Hereby, an unwanted collision between thecollimator (106, 206, 306) and the compression paddle (107 a, 107 b; 207a, 207 b; 307 a, 307 b) is avoided. In another embodiment, the controlunit (121, 221, 321) is adapted to control the movement of the x-raysource (104, 204, 304) and the detector (105, 205, 305) such that theangle α of the scan arm (103, 203, 303) does not exceed a limit value,wherein the limit value is constantly varying with the positions of thex-ray source (104, 204, 304) along a first movement path and thedetector (105, 205, 305) along a second movement path and based on theheight position of the compression paddle (107 a, 107 b; 207 a, 207 b;307 a, 307 b). For instance, in addition to the general control of thescan arm (103, 203, 303) to allow a smaller angle α due to a highposition of the compression paddle (107 a, 107 b; 207 a, 207 b; 307 a,307 b), a relatively higher position of the scan arm (103, 203, 303)would allow a somewhat larger angle than a relatively lower position ofthe scan arm (103, 203, 303), wherein the collision between thecollimator (106, 206, 306) and the compression paddle (107 a, 107 b; 207a, 207 b; 307 a, 307 b) would still be prevented.

According to another embodiment of the invention, the detector (105,205, 305) is adapted to sense characteristics of a received x-ray beam(122, 222, 322) from the x-ray source (104, 204, 304) in real timeduring the entire scan movement. The detector (105, 205, 305) is furtheradapted to output said data wherein the control unit (121, 221, 321)controlling the movement of the x-ray source (104, 204, 304) and thedetector (105, 205, 305) is connected to the detector (105, 205, 305) byfor instance a cable (124, 224, 324) or wireless transmission whereinsaid data, also referred to as external data, can be received by thecontrol unit (121, 221, 321), wherein the control unit (121, 221, 321)uses said external data for controlling a remainder of the scanmovement.

As seen in FIG. 8 a, the detector (105, 205, 305) has a first (105 b,205 b, 305 b) and second end (105 c, 205 c, 305 c) wherein a pluralityof detector lines (125) are arranged between said first and second ends.The detector (105, 205, 305) is adapted to receive impinging photonsfrom the x-ray source (104, 204, 304) during a scan movement, and thedetector (105, 205, 305) is further being adapted to count each photonimpinging on the detector (105, 205, 305) above a certain energythreshold by generating a signal corresponding to the energy of eachimpinging photon. During a scan of an object, fewer impinging photonsper time frame above said threshold will reach the detector (105, 205,305) compared to the rest of the scan movement when no object (108, 208,308) placed in the x-ray beam in order to be scanned, attenuates photonsfrom the x-ray beam. In other words, the x-ray intensity, or count rate,of the photons is lower once a scan of an object (108, 208, 308) startscompared to the rest of a scan movement. Other methods of establishingor detecting the x-ray intensity is also known in the art, such as forinstance measuring the total charge readout at during a time frame etc.According to this embodiment, such information is used by the controlunit (121, 221, 321) for controlling the movement of the x-ray source(104, 204, 304) and the detector (105, 205, 305). In the same figure ascan movement of an x-ray source (104, 204, 304) and a detector (105,205, 305) is illustrated along with an object (108, 208, 308) compressedbetween two compression paddles (107 a, 107 b; 207 a, 207 b; 307 a, 307b) is seen wherein the scan arm (103, 203, 303) moves to the left with acertain speed. The scan movement shown has just recently become a scanof an object. This phase of the scan movement is sensed by the detectorlines (105 a, 205 a, 305 a) being arranged closer to the first end ofthe detector (105, 205, 305), arranged essentially in the left part ofthe detector (105, 205, 305) as they sense a lower count rate due to theattenuation of photons in the object. This information, or data, is sentto the control unit (121, 221, 321) for controlling the remainder of thescan motion. As seen in FIG. 8 b, according to one embodiment, the speedof at least the x-ray source (104, 204, 304) thereby decreases duringthe remainder of the scan of the object (108, 208, 308) to a presetspeed which is related to the actual count rate sensed by the detector(105, 205, 305). Essentially, the speed of the x-ray source will belowered even more than the x-ray source during a scan of an object, suchthat a higher ratio between the speed of the x-ray source and thedetector is achieved. Hereby, the tomographic angles for each point inthe object is increased, which is relevant when reconstructingtomosynthesis images over the relevant object. At the same time, byallowing a having a higher speed of the x-ray source and the detectorduring a scan movement which is not an object scan, time for performingthe entire scan movement will be decreased. This is beneficial not theleast when considering the large amount of investigations that need tobe performed during a mammographic screenings. Data concerning therelationship between sensed count rate and speed may be saved in a tableformat into a memory device of in or in connection to the control unit(121, 221, 321) and used by the control unit (121, 221, 321) uponcontrolling the movement. In any part of the scan movement that is not ascan of the object, the speed of the at least the x-ray source (104,204, 304) may be increased again before the scan of the object (108,208, 308) in order to lower the time required to perform the scan.Further, the control unit (121, 221, 321) is adapted to control themovement of the x-ray source (104, 204, 304) and the detector (105, 205,305) such that the ratio between their respective speeds are high enoughto allow the x-ray source (104, 204, 304) to pass the detector (105,205, 305) in a horizontal direction during the scan of an object (108,208, 308) as sensed by the detector (105, 205, 305).

According to another embodiment of the invention, as seen in FIG. 9, thecontrol unit (121, 221, 321) is further adapted to control the movementof the x-ray source (104, 204, 304) and the detector (105, 205, 305)based on the detector (105, 205, 305) identifying an interesting area ofthe object, e.g. a suspected abnormality in a breast, wherein a certainpredefined scan movement is performed or wherein the speed of at leastthe x-ray source (104, 204, 304) decreases to enhance ability to furtheranalyze this area. The interesting area is seen as a dark spot in theobject (108, 208, 308) This identification may be performed during theactual scan of the object, but may also have been performed during aprevious scan directly before-hand, or alternatively at a differentscreening at a time when an interesting area in an object wasidentified. The positions of the x-ray source and the detector forperforming a scan movement over this area alone requires saving of datacorresponding to these predefined positions. In the latter cases, theexternal data used by the control unit (121, 221, 321) may be saved intoa database wherein this database is accessible by the control unit (121,221, 321). These type of scans performed over an interesting spot isnormally referred to as a spot scan. According to one embodiment, thex-ray source and the detector decreases their both their speeds whenreaching the interesting area, in such way that the ratio between thespeed of the x-ray source and the detector increases such that largertomographic angles are achieved.

What is said above for the capacity of the detector (105, 205, 305) tosense when an object (108, 208, 308) is scanned can be implemented andused together with any of the embodiments described in connection to thecontrolling of the movement based on the presence of a compressionpaddle.

In the following, different scan movements will be described, that mayserve to optimize the tomo-angles based on external data according tocertain embodiments:

FIG. 10 a-FIG. 10 e illustrates a schematic view of the scan arm (103,203, 303) comprising an x-ray source (104, 204, 304) and the detector(105, 205, 305) and one preferred scan movement. The directions andsizes of the arrows represent the directions and speed of the x-raysource (104, 204, 304) and the detector (105, 205, 305). A lack ofarrows represents a zero speed of the x-ray source or the detector.Turning points of the x-ray source and the detector comprises a positionwherein the x-ray source or detector changes direction from a first to asecond direction wherein the second direction is essentially oppositethe first direction. In FIG. 10 a, both the x-ray source (104, 204, 304)and the detector (105, 205, 305) travel to towards their first turningpoints, wherein the x-ray source (104, 204, 304) has a speed than thedetector (105, 205, 305), i.e. wherein the ratio between the speed ofthe x-ray source (104, 204, 304) and the detector (105, 205, 305) isaround 2. In FIG. 10 b, the x-ray source (104, 204, 304) has passed thedetector (105, 205, 305) in a horizontal direction due to the higherspeed. In FIG. 10 c, the x-ray source (104, 204, 304) has reached thefirst turning point along the first movement path, whereas the detector(105, 205, 305) continues a movement towards the first turning pointalong the second movement path. In FIG. 10 d the x-ray source (104, 204,304) turns direction essentially into an opposite direction as prior toreaching the turning point, wherein the speed of the x-ray source (104,204, 304) is increased to a similar speed had prior to reaching theturning point, essentially instantaneously after turning This requires arelatively high acceleration of x-ray source (104, 204, 304), accordingto one embodiment, the acceleration is in the range of 1 m/s². In thesame scan, the x-ray source (104, 204, 304) and the detector (105, 205,305) may travel towards the second turning points along the first andsecond movement paths and perform a corresponding motion as describedabove.

FIG. 10 e represents the scan movement of FIG. 10 a-10 d wherein theachieved tomo-angle is shown. The movement of the x-ray source along afirst movement path and the movement of the detector along the secondmovement path, corresponds to a combined movement path, wherein saidcombined movement path can be represented by a curve through amulti-dimensional parametric space involving a position along one axisand an angle between said x-ray source and detector as seen in thefigure. The three dots (125) represents the position of a bundle ofthree x-rays, corresponding to three detector lines (125) of thedetector (105, 205, 305), thus impinging into the detector (105, 205,305) with three different angles, wherein the middle ray impinges thedetector (105, 205, 305) with an angle=0. The position along the object(108, 208, 308) being scanned is represented by the x-axis. The varyingray angle of the x-ray source (104, 204, 304) and the detector (105,205, 305) relative a vertical line corresponding to the middle ray ofthe three shown rays impinging on the detector (105, 205, 305) is shownalong the y-axis v_(r,), and thus implicitly represents a position ofthe x-ray source (104, 204, 304) in relation to the detector (105, 205,305). The tomo-angle achieved during a scan movement between twoposition of the x-ray detector (105, 205, 305) is represented by thedistance v_(t,), i.e. the spread of local tomographic projection angles.

The lowermost position to the left of the three dots (125), i.e. in thethird quadrant, corresponds to FIG. 5 a, wherein the detector (105, 205,305) is slightly to the left of the detector (105, 205, 305) scanning aleft portion of the object. The position of the three detector lines(125) in the second quadrant represents a position of the scan arm (103,203, 303) corresponding to that shown in FIG. 10 c, i.e. when the x-raysource reaches the turning point. FIG. 10 b would correspond to aposition between that just described and the x-axis. FIG. 10 dcorresponds to a position in origo of wherein v_(r) is zero and themiddle of the object (108, 208, 308) is scanned. The continued scanmovement towards the right portions of the object, are represented bythe dots (125) in the first and fourth quadrants. This part of the scanmovement is not further explained here as it is a mirroring of themovement in the just described. From FIG. 10 e, the importance of theratio between the speeds of the x-ray source (104, 204, 304) and thedetector (105, 205, 305) is seen for the tomo-angle. The larger theratio, and hence the steepness of the lines between two positions of thedetector (105, 205, 305), the larger the tomo-angle can be achieved.Hence, the scan movement right after the x-ray source turns, wherein thex-ray source (104, 204, 304) is sharply accelerated, is essential forachieving large and optimized tomo-angles.

FIG. 11 a-FIG. 11 d represents a similar scan movement to that describedin FIG. 10 a-10 d, with the difference that the detector (105, 205, 305)reaches the first turning point before the x-ray source (104, 204, 304).The scan movement is therefore not further explained here.

FIG. 12 a-12 g illustrates a schematic view of the scan arm (103, 203,303) comprising an x-ray source (104, 204, 304) and the detector (105,205, 305) and another preferred scan movement. The directions and sizesof the arrows represent the directions and speed of the x-ray source(104, 204, 304) and the detector (105, 205, 305). In FIG. 12 a, both thex-ray source (104, 204, 304) and the detector (105, 205, 305) travel totowards their first turning points, wherein the x-ray source (104, 204,304) has a higher speed than the detector (105, 205, 305). In FIG. 12 b,the x-ray source (104, 204, 304) has passed the detector (105, 205, 305)in a horizontal direction due to the higher speed and reached a turningpoint of the first movement path, wherein the detector (105, 205, 305)continues the movement towards its first turning point along a secondmovement path. In FIG. 12 c the x-ray source (104, 204, 304) turnsdirection essentially in an opposite direction as prior to reaching theturning point, wherein the speed of the x-ray source (104, 204, 304) isincreased to a similar speed had prior to reaching the turning point,essentially instantaneously after the turning. This requires a highacceleration of x-ray source (104, 204, 304), in the range of 1 m/s². Inthe same figure, the detector (105, 205, 305) continues the movementtowards its first turning point along a second movement path. In FIG. 12d the x-ray detector (105, 205, 305) has reached its first turning pointalong the second movement path, and essentially simultaneously, themovement of the x-ray source (104, 204, 304) along the first movementpath is stopped. In FIG. 12 e, the x-ray source (104, 204, 304) againaccelerates steeply towards the first turning point, whereinsimultaneously, the detector (105, 205, 305) moves towards the secondturning point along the second movement path, accelerating steeply. InFIG. 12 f, the x-ray source (104, 204, 304) and the detector (105, 205,305) has moved along their essentially opposite directions, such thatthe x-ray is now closer to the first turning point than the detector(105, 205, 305). i.e. the angle v, is again positive.

In the same scan, the x-ray source (104, 204, 304) and the detector(105, 205, 305) may travel towards the second turning points along thefirst and second movement paths and perform a corresponding motion asdescribed above.

FIG. 12 g represents the scan movement of FIG. 12 a-12 e wherein theachieved tomo-angle is shown with references similar to those describedin FIG. 10 e. The lowermost position to the left of the three dots(125), i.e. in the third quadrant, corresponds to FIG. 12 a, wherein thedetector (105, 205, 305) is slightly to the left of the detector (105,205, 305) scanning a left portion of the object. The position of thethree detector lines (125) in the second quadrant represents a positionof the scan arm (103, 203, 303) corresponding to that shown in FIG. 12b, i.e. when the x.-ray source reaches the turning point. FIG. 12 d,wherein the detector (105, 205, 305) has reached its turning point alongthe second movement path corresponds to essentially the same position aswhen the scan started, i.e. the dots (125) are overlapping the dots(125) in the third quadrant. The movement in opposite direction by thex-ray source (104, 204, 304) and the detector (105, 205, 305) such thatthe x-ray is now closer to the first turning point than the detector(105, 205, 305) corresponding to FIG. 12 f is represented by the secondset of three dots (125) in the second quadrant positioned slightly tothe right and with a little smaller angle v_(r). Through this scanmovement, a uniform tomo-angle around the turning point can be achieved,wherein v_(t2)=v_(t0). Compared for instance with v_(t1), which issimilar to the tomo-angles as achieved in the turning points in FIG. 12g, and smaller than v_(t0). Without the scan movement according to FIG.7 g, the image quality will be poorer for this part of the object. A bigtomo-angle is achieved in a left part of the scan corresponding to theposition of FIG. 12 f, i.e. left of the v_(t2) position. As can furtherbe seen in the same figure, the right part of the scan is differentcompared to the left part of the scan, wherein the detector (105, 205,305) is not changing direction in its second turning point. It thuscorresponds to the right part of the scan as seen in FIG. 10 e. It canfurther be noted that some of the angles are scanned twice in the leftpart of the scan seen by the overlapping of rays. The scanning of suchsuperfluous angles can be masked by a suitable field limiter coveringthe relevant detector lines (105 a, 205 a, 305 a).

FIG. 13 shows an alternative scan movement, wherein the tomo-angle isslightly smaller compared to in FIG. 12 g. This is achieved by reducingthe relative speed between the x-ray source (104, 204, 304) and thedetector (105, 205, 305), i.e. the ratio between the speed of the x-raysource and the detector. Such scan movement may be preferred and optimalfor a relatively thicker breast, wherein aliasing problems may occur ifthe tomo-angles are to large. Thus, the control unit may use theexternal data such as the position of the compression paddle, or dataconcerning x-ray intensity, to move the x-ray source and detectoraccording to this scan movement.

FIG. 14 a-FIG. 14 f represents a similar scan movement to that describedin FIG. 12 a-12 f, with the difference that the detector (105, 205, 305)reaches the first turning point before the x-ray source (104, 204, 304).The scan movement is therefore not further explained here.

FIG. 15 a-15 e illustrates a schematic view of the scan arm (103, 203,303) comprising an x-ray source (104, 204, 304) and the detector (105,205, 305) and yet another preferred scan movement wherein a limited 2Dscan is performed around the first turning point. FIG. 15 a shows thex-ray source (104, 204, 304) and the detector (105, 205, 305) movingtowards the first turning point. In FIG. 15 b, the x-ray source (104,204, 304) has reached the first turning point and stops there whereinthe detector (105, 205, 305) continues to move towards its first turningpoint. FIG. 15 c shows a position wherein both the x-ray source (104,204, 304) and the detector (105, 205, 305) has reached their firstturning points and wherein a 2D scan has been performed during betweenthe positions of FIGS. 15 b and 15 c since no movement of the x-raysource (104, 204, 304) takes place. In FIG. 15 d, the x-ray source (104,204, 304) accelerates steeply upon the detector (105, 205, 305) reachingits first turning point. FIG. 15 e represents a position wherein thedetector (105, 205, 305) has started to move towards the second turningpoint after a certain time.

FIG. 16 a-16 e represents a similar scan movement to that described inFIG. 15 a-15 f, with the difference that the detector (105, 205, 305)reaches the first turning point before the x-ray source (104, 204, 304).The scan movement is therefore not further explained here.

According to an embodiment of the invention, wherein the control unit isadapted to control the movement of the x-ray source such thattomosynthetic scan movements occur, optimization of tomo-angles isachieved by the control unit controlling the movement of the x-raysource and the detector at every instant in time during a scan movement,wherein a scan of an object occurs. Every adaptation of the speeds anddirections of the x-ray source and the detector described herein may bedescribed as an optimization of the tomo-angle, including the highacceleration occurring after the x-ray source or the detector reaches aturning point, wherein external data such as the position of the atleast one compression paddle in relation to the detector or collimator,characteristics of the breast such as boundary, thickness, orattenuation resulting from the thickness of the breast sets limitationsto achieving the most optimal tomo-angle, i.e. the angle of the scan armwhen passing the compression paddle, speed ratio between the x-raysource and the detector, etc.

FIG. 17 shows a scan arm 103, 203, 303 and a field limiting device 140,240, 340 according to one embodiment in a position where the angle ofthe scan arm 103, 203, 303 in relation to a vertical line is zero. Anx-ray source 104, 204, 304 adapted to emit x-ray radiation in an x-raybeam is arranged in a first position 147, 247, 347 of the scan arm 103,203, 303 corresponding to a first end of the scan arm 103, 203, 303. Adetector 105, 205, 305 is arranged in a second position 148, 248, 348 ofthe scan arm 103, 203, 303 corresponding to a second end of the scan arm103, 203, 303, and adapted to receive the x-ray beam from the x-raysource. A section of the object 108, 208, 308 table is seen in FIG. 19comprising an image field 149, 249, 349, having a first end 145, 245,345 and a second end 146, 246, 346.

The field limiting device 140, 240, 340 comprises at least a portionthereof being arranged essentially between the x-ray source 104, 204,304 and the detector 105, 205, 305, preferably in a third position ofthe scan arm 103, 203, 303 at least during certain positions of thefield limiting device. The third position of the scan arm corresponds toa position on the scan arm such that a movement of the x-ray source 104,204, 304 causes a movement of the field limiting device 140, 240, 340.According to another embodiment, the scan arm 103, 203, 303 is notpresent, wherein no mechanical connection means connect the x-ray source104, 204, 304, detector and field limiting device but these are adaptedto move independently of the movements of each other.

The field limiting device 140, 240, 340 comprises a first side portion140 a, 240 a, 340 a and a second side portion 140 b, 240 b, 340 b and anopening 141, 241, 341 there between, wherein the x-ray radiation fromthe x-ray source 104, 204, 304 is allowed to pass through the opening141, 241, 341 but is blocked by being essentially absorbed by the first140 a, 240 a, 340 a and second side portion 140 b, 240 b, 340 b.Preferably, the first 140 a, 240 a, 340 a and second side portions 140b, 240 b, 340 b are made of an x-ray opaque material such as steeland/or lead to increase the absorbing capacity. The first 140 a, 240 a,340 a and second 140 b, 240 b, 340 b side portions are adapted to beadjustably movable towards a center line of the x-ray radiation fieldbetween a first and a second position, wherein the first 140 a, 240 a,340 a and second 140 b, 240 b, 340 b side portions prevent a largershare of the x-ray radiation from passing the field limiting device 140,240, 340 in a second position than in a first position. Preferably, themovement of the first 140 a, 240 a, 340 a and second 140 b, 240 b, 340 bside portions is enabled by at least one linear rail upon which thefirst 140 a, 240 a, 340 a and second side portions 140 b, 240 b, 340 bare adapted to slide. A driving means, preferably an electrical motordrives the first 140 a, 240 a, 340 a and second 140 b, 240 b, 340 b sideportions and controls the movement thereof, wherein the electrical motoris controlled by a first control unit 150, 250, 350. The first 140 a,240 a, 340 a and second 140 b, 240 b, 340 b side portions are adapted tobe moved into any position between the first 140 a, 240 a, 340 a andsecond positions wherein the first 140 a, 240 a, 340 a and second 140 b,240 b, 340 b side portions prevent a larger share of the x-ray radiationfrom passing the field limiting device 140, 240, 340 in any suchposition compared to the first position.

As seen in FIG. 17, the opening 141, 241, 341 of the field limitingdevice 140, 240, 340 comprises a first angle v_(f1) from the center line142, 242, 342 of the x-ray beam to the end 143, 243, 343 of the firstside portion 140 a, 240 a, 340 a seen from the x-ray source 104, 204,304, a second angle v_(f2) from a center line 142, 242, 342 of the x-raybeam to the end 144, 244, 344 of the second side portion 140 b, 240 b,340 b seen from the x-ray source 104, 204, 304. Further, v_(i2) is theangle from a center line 142, 242, 342 of the x-ray beam to the secondimage end 146, 246, 346 seen from the x-ray source 104, 204, 304, andv_(i1) is the angle from a center line 142, 242, 342 of the x-ray beamto the first image end 145, 245, 345 seen from the x-ray source 104,204, 304. Angle v_(d2) is defined as the angle from a center line 142,242, 342 of the x-ray beam to a second end 105 c, 205 c, 305 c of thedetector 105, 205, 305 seen from the x-ray source 104, 204, 304, andangle v_(d1) is defined as the angle from a center line 142, 242, 342 ofthe x-ray beam to a first end 105 b, 205 b, 305 b of the detector 105,205, 305 seen from the x-ray source 104, 204, 304.

The x-ray source 104, 204, 304 is adapted to be moved in relation to afirst portion of the x-ray apparatus 102, 202, 302, and the detector105, 205, 305 is adapted to be moved in relation to a first portion ofthe x-ray apparatus 102, 202, 302. In order for the x-ray source 104,204, 304 and the detector 105, 205, 305 to be in line with each other,i.e. such that an x-ray beam emitted from the x-ray source is receivedby the detector 105, 205, 305, wherein the x-ray beam is directedessentially towards the detector 105, 205, 305 during the movement ofthe x-ray source 104, 204, 304 and the detector 105, 205, 305, the x-raysource and the detector 105, 205, 305 are adapted to rotate in relationto first portion of the x-ray apparatus 104, 204, 304. A control unit121, 221, 321 is adapted for controlling the movement of the x-raysource and the detector. According to one embodiment the control unit isreferred to as a second control unit 121, 221, 321. According to anotherembodiment, the first and second control unit are comprised by the samecontrol unit.

The first portion of the x-ray apparatus is referred to as a fixedportion at any point of the x-ray apparatus, i.e. portion that isessentially non movable, and is thus a fixed position in space.

The second control unit may control the movement of the x-ray source104, 204, 304 and the detector such that the second control unit 121,221, 321 is adapted to change direction of the x-ray source 104, 204,304 and the detector at a first turning point of the x-ray source, and afirst turning point of the detector respectively, wherein the x-raysource and the detector move in a second direction after reaching thefirst turning point which is essentially opposite a first directionprior to reaching the first turning point.

According to one embodiment, the detector comprises a plurality ofdetector lines, wherein the first control unit is adapted to calculatethe angles of the x-ray beam towards each of the detector lines inrelation to a vertical line at predefined positions along a pathessentially extending in a horizontal direction, based on the positionsignals from the position sensing arrangement. The first control unit150, 250, 350 is adapted to save the calculated angles, preferably in atable format in a memory device in the first control unit. Essentially,the saved calculated angles may comprise a list of angles for eachmillimetre along the path, wherein the path may comprise a straight linealong the object table, or a curve at a location within the distancefrom the object table to a compression paddle depending on scanmovement. The first control unit 150, 250, 350 is adapted to control atleast the first side portion of the field limiting device to prevent thex-ray beam from being received by the detector lines more than once foreach calculated angle at each predefined position along the pathessentially extending in a horizontal direction. Since the angles mayreoccur due to the change of directions of the x-ray source and thedetector at the first turning point, for instance, this is a relevantfeature to further reduce the x-ray radiation dose since scanning thesame angle twice would not improve the image of the breast, but would besuperfluous.

Prior to initiating a scan movement of the x-ray source and thedetector, the first control unit may establish the table of calculatedangles that will be generated during a main scan movement and thecalculated angles that will be generated during a bouncing scan movementoccurring at around at least the first turning point. The first controlunit 150, 250, 350 may assign binary number 1 for each angle generatedduring a bouncing scan movement that is generated also during the mainscan movement, i.e. wherein there is an overlap, and assign a binarynumber 0 for each angle generated during a bouncing scan movement thatis not generated during the main scan movement. The first control unitis adapted to control at least the first side portion such that itblocks the x-ray beam from radiating detector lines that has beenassigned a binary 1 but not a binary 0 during a bouncing scan movement.

According to one embodiment, a main scan movement comprises the movementof the x-ray source 104, 204, 304 and the detector before the x-raysource reaches the first turning point and after the detector reachesthe first turning point.

According to one embodiment, the bouncing scan movement comprises themovement of the x-ray source 104, 204, 304 and the detector from whenthe x-ray source reaches the first turning point until the detectorreaches the first turning point, or, alternatively, from when the x-raysource 104, 204, 304 reaches the first turning point, the detectorreaches the first turning point, and until the x-ray source 104, 204,304 reaches a second turning point wherein the x-ray source 104, 204,304 changes direction of movement again, essentially moving in the firstdirection.

According to one embodiment, the first control unit is adapted tocontrol the movement of at least the first side portion during aCC-scan, also known as Cranio caudial scan, wherein only a specificportion a breast is scanned, such as to limit the size of the imagefield during the scan movement by the size of the opening between thefirst and second side portions, wherein radiation of an x-ray beam isprevented outside the image field during such scan movement. Anothertype of scan wherein such limitation of the image field by thecontrolling of at least the first side portion is the MLO-scan, Mediallateral oblique scan movement.

FIG. 18 a shows the scan arm 103, 203, 303 with a field limiting device140, 240, 340 according to a one embodiment wherein the x-ray source104, 204, 304 has moved along an arbitrary first movement path, and thedetector 105, 205, 305 has moved, for instance along a arbitrary secondmovement path towards the first turning points in the first and secondmovement paths, into a position such that v_(d1) is larger than v_(i1),or in other words, such that the x-ray beam extends outside the firstimage field 149, 249, 349 provided that no field limiting device 140,240, 340 is used. Naturally, such x-ray beam radiation does notcontribute to enhancing the mammographic images and an object 108, 208,308 is therefore to reduce such radiation. As disclosed in FIG. 18 a,the first side portion 140 a, 240 a, 340 a has moved slightly towards asecond position in order to prevent x-ray radiation from irradiating anarea outside the first image end 145, 245, 345. The first control unit150, 250, 350 is adapted to control the movement of the first 140 a, 240a, 340 a and second side portion 140 b, 240 b, 340 b based on datastored in a memory means of the control unit 150, 250, 350, the datacomprising information regarding the necessary positions of the first140 a, 240 a, 340 a and second side portions 140 b, 240 b, 340 b basedon the positions of the x-ray source 104, 204, 304 and the detector 105,205, 305. In order to sense the positions of the x-ray source and thedetector, a position sensing arrangement is provided as describedherein, comprising any or all of first position sensing device 173, 273,373, second position sensing device 172, 272, 372, third positionsensing device 178, 278, 378, fourth position sensing device 171, 271,371, fifth position sensing device 170, 270, 370, sixth position sensingdevice 180, 280, 380 or combination thereof. Any other type of positionsensing device may be used that in a direct or indirect manner is ableto sense or deduce the positions of the x-ray source 104, 204, 304 andthe detector 105, 205, 305.

The first control unit is further adapted for receiving the positionsignals from the position sensing arrangement wherein the first controlunit is adapted to control the movement of at least the first sideportion based on the position signals. According to one embodiment, thefirst control unit may be equal to the recording device 179, 279, 379.

In an analogous manner, as seen in FIG. 18 b, the second side portion140 b, 240 b, 340 b is adapted to move towards a second position inorder to prevent x-ray radiation from irradiating an area outside thesecond image end 146, 246, 346.

FIG. 18 c discloses the scan arm 103, 203, 303 with a field limitingdevice 140, 240, 340 according to one embodiment wherein the x-raysource 104, 204, 304 and the detector 105, 205, 305 have moved alongtheir movement paths towards a first turning point into a position suchthat v_(d1) is smaller than v_(i1), or in other words, such that thex-ray radiation field extends outside the first detector end 105 b, 205b, 305 b provided that no field limiting device 140, 240, 340 is used.As in the case of FIG. 18 a, such radiation would not contribute toenhancing the mammographic images and must be blocked. Therefore, asseen in FIG. 18 c, the first side portion 140 a, 240 a, 340 a has movedtowards a second position in order to prevent x-ray radiation fromirradiating an area outside the first detector end 105 b, 205 b, 305 b.In an analogous manner, as seen in FIG. 18 d, the second side portion140 b, 240 b, 340 b is adapted to move towards a second position inorder to prevent x-ray radiation from irradiating an area outside thesecond detector end 105 c, 205 c, 305 c.

Thus, concluding the synchronized field limiting device 140, 240, 340movements of FIG. 18 a-FIG. 18 d, the first control unit 150, 250, 350is adapted to control the movement of the first side portion 140 a, 240a, 340 a if v_(i1)<v_(d1) such that v_(f1)≦v_(i1), if v_(i1)>v_(d1) suchthat v_(f1)≦v_(d1) and the movement of the second side portion 140 b,240 b, 340 b if v_(i2)<v_(d2) such that v_(f2)≦v_(i2), if v_(i2)>v_(d2)such that v_(f2)≦v_(d2).

Naturally, the first 140 a, 240 a, 340 a and second side portions 140 b,240 b, 340 b are adapted to move between the first 140 a, 240 a, 340 aand second positions based on a movement of the x-ray source 104, 204,304 and the detector 105, 205, 305, and the direction of the movement ofthe side portions are related to the movement direction of x-ray source104, 204, 304 and the detector 105, 205, 305. Thus, the first sideportion 140 a, 240 a, 340 a is adapted to move towards the secondposition if v_(i1) is decreasing, and adapted to move towards the firstposition if v_(i1) is increasing. The second side portion 140 b, 240 b,340 b is hence adapted to move towards a second position if v_(i2) isdecreasing and towards a first position if v_(i2) is increasing.

FIG. 19 a discloses another embodiment of the scan arm 103, 203, 303with a field limiting device 140, 240, 340 wherein the field limitingdevice 140, 240, 340 comprises a cylindrical device 151, 251, 351 havingan aperture, wherein the portion of the cylindrical device 151, 251, 351defining a first end of the aperture comprises a first side portion 140a, 240 a, 340 a, and the portion of the cylindrical device 151, 251, 351defining a second end of the aperture comprises the second side portion140 b, 240 b, 340 b. The cylindrical field limiting device 140, 240, 340is pivotally arranged for rotation around the x-ray source 104, 204,304.

The first control unit 150, 250, 350 is adapted to rotate thecylindrical device 151, 251, 351 based on the positions of the x-raysource 104, 204, 304 and the detector 105, 205, 305, for instance alongtheir first 140 a, 240 a, 340 a and second movement paths in ananalogous manner to the embodiment described in FIG. 17-19, and whereinthe references to angles are identical. The position of the x-ray source104, 204, 304 and the detector 105, 205, 305 as seen in FIG. 19 aresults in a relationship between the angles such that v_(i2)<v_(f2),before rotation of the field limiting device 140, 240, 340, wherein, asa result, the cylindrical device 151, 251, 351 is adapted to rotate anangle v_(rot2)=(v_(f2)−v_(i2)) resulting in a movement of the first 140a, 240 a, 340 a and second end of the aperture moving towards a secondposition, to prevent x-ray radiation from irradiating an area outsidethe second image end 146, 246, 346. In an analogous manner, as seen inFIG. 19 b, the cylindrical device 151, 251, 351 is adapted to rotatetowards a second position v_(rot1)=(v_(f1)−v_(i1)), if v_(i1)<v_(f1), inorder to prevent x-ray radiation from irradiating an area outside thefirst image end 145, 245, 345.

It should be noted that, according to one embodiment, the second sideportion 140 b, 240 b, 340 b is adapted to move towards a first position,a second position or not move, as the first side portion 140 a, 240 a,340 a moves towards the second position, wherein the second side portion140 b, 240 b, 340 b prevents a larger share of the x-ray radiation frompassing the field limiting device 140, 240, 340 in a second positionthan in a first position.

FIG. 20 illustrates schematically an x-ray imaging system 101, 201, 301according to one embodiment, wherein the system comprises an x-rayapparatus 102, 202, 302. The x-ray apparatus 102, 202, 302 comprises ascan arm 103, 203, 303, wherein an x-ray source 104, 204, 304 isarranged on one upper end of the scan arm but may be arranged at anyposition along the scan arm 103, 203, 303 according to other embodimentsof the invention. A detector is arranged in the other 105, 205, 305,lower end of the scan arm 103, 203, 303, wherein the detector comprisesa plurality of detector strips 105 a, 205 a, 305 a, each detector stripbuilt up by a plurality of detector pixels. The detector 105, 205, 305may however be arranged at any position along a scan arm 103, 203, 303according to other embodiments of the invention. A collimator 106, 206,306 comprising a plurality of slits is arranged between the x-ray sourceand the detector on the scan arm 103, 203, 303.

FIG. 20 further shows a schematic view of the x-ray apparatus 102, 202,302, wherein the arrangement and parts of the apparatus that enablesboth 2D scan motions and 3D scan motions are further explained. As seenin the figure, in a position slightly below the x-ray source 104, 204,304, the scan arm is pivotally arranged in a first end of a firstsuspension arm 109, 209, 309. The pivot point may be arranged in thecenter of the x-ray source 104, 204, 304, and the first end 109 a, 209a, 309 a of the first suspension arm 109, 209, 309 may be pivotallyarranged in an upper x-ray source portion 104 a, 204 a, 304 a.

As seen in FIG. 21, the second end 109 b, 209 b, 309 b of the firstsuspension arm 109, 209, 309 is arranged linearly displaceable inrelation to a first end 110 a, 210 a, 310 a of a second suspension arm110, 210, 310, in a manner such that the total length of the first 109,209, 309 and second suspension arm 110, 210, 310 may be varied.According to one embodiment, the first suspension arm 109, 209, 309 isarranged partly inside the second suspension arm 110, 210, 310, howeverthe arrangement may be the other way around, i.e. wherein the secondsuspension arm 110, 210, 310 is partly arranged inside the firstsuspension arm 109, 209, 309. A motor 177, 277, 377 is adapted to a thelinear screw 115, 215, 315 arrangement and thereby actuate the lineardisplacement of the first and suspension arms. Further, the second end110 b, 210 b, 310 b of the second suspension arm 110, 210, 310 ispivotally arranged in a lower portion 111, 211, 311 of the x-rayapparatus.

FIG. 22 shows a side view of the x-ray apparatus. In order to controlthe rotational movement of the scan arm 103, 203, 303 in relation to thefirst suspension arm 109, 209, 309, a first motor 116, 216, 316,preferably of electrical kind, is arranged, preferably on the firstsuspension arm 109, 209, 309, wherein a first sprocket 117, 217, 317 isadapted to be rotated upon the activation of the first motor 116, 216,316 in one of two rotational directions. A second sprocket 118, 218,318, preferably larger than the first sprocket 117, 217, 317, isarranged on the scan arm 103, 203, 303 in order to be engaged by thefirst sprocket 117, 217, 317, wherein a rotational movement of the firstsprocket 117, 217, 317 is transferred to generate a rotational movementof the second sprocket 118, 218, 318 and the scan arm 103, 203, 303. Thesecond sprocket 118, 218, 318 is arranged on a pivot axis 175, 275, 375,adapted to be rotated in relation to the first suspension arm 109, 209,309 and extends through the first suspension arm 109, 209, 309. At oneend of the pivot axis 175, 275, 375, a first position sensing device173, 273, 373 is arranged. The first position sensing device 173, 273,373 comprises a first rotary position encoder 173, 273, 373. The firstrotary position encoder 173, 273, 373 comprises a rotary portion 173 b,273 b, 373 b arranged on an end of the pivot axis 175, 275, 375, and asensing portion 173 a, 273 a, 373 a arranged on the first suspension arm109, 209, 309, wherein the sensing portion 173 a, 273 a, 373 a isadapted to sense the relative rotational position of the rotary portion173 b, 273 b, 373 b and hence the actual relative rotational position ofthe scan arm 103, 203, 303 in relation to the first suspension arm 109,209, 309.

A second motor 126, 226, 326, preferably an electrical motor and similarto the first motor 116, 216, 316, is arranged in the lower portion 111,211, 311 or in another part of the x-ray apparatus 102, 202, 302,wherein a third sprocket 120, 220, 320 is arranged to be rotated uponthe activation of the motor in one of two rotational directions. Afourth sprocket 120, 220, 320, preferably larger than the third sprocket119, 219, 319, is arranged on the second suspension arm 110, 210, 310 inorder to be engaged with the third sprocket 119, 219, 319, wherein arotational movement of the third sprocket 119, 219, 319 is transferredto generate a rotational movement of the fourth sprocket 120, 220, 320and the second suspension arm 110, 210, 310. The fourth sprocket 120,220, 320 is arranged on a pivot axis 174, 274, 374, adapted to berotated in relation to the lower portion 111, 211, 311 and extendsthrough the lower portion 111, 211, 311. At one end of the pivot axis174, 274, 374, a second position sensing device 172, 272, 372 isarranged. The second position sensing device 172, 272, 372 comprises asecond rotary position encoder 172, 272, 372. The second rotary positionencoder 172, 272, 372 comprises a rotary portion 172 b, 272 b, 372 barranged on an end of the pivot axis 174, 274, 374, and a sensingportion 173 a, 273 a, 373 a arranged on the lower portion 111, 211, 311,wherein the sensing portion 173 a, 273 a, 373 a is adapted to sense therelative rotational position of the rotary portion 173 b, 273 b, 373 band hence the actual relative rotational position of the secondsuspension arm 110, 210, 310 in relation to the lower portion 111, 211,311.

A third position sensing device 178, 278, 378 comprising a linearposition encoder 178, 278, 378 is adapted to sense the actual relativelinear position between the second end 109 b, 209 b, 309 b of the firstsuspension arm 109, 209, 309 and the first end 210 a, 210 a, 310 a ofthe second suspension arm 110, 210, 310, and hence the total length ofthe first and second suspension arms. The linear position encoder 178,278, 378 comprises a position sensor 178 a, 278 a, 378 a arranged oneither of the first or the second suspension arm, and a scale for aposition sensor is arranged on the other of the first or secondsuspension arm.

A fourth position sensing device 171, 271, 371 is adapted to sense therelative rotational position of a rotor 116 a, 216 a, 316 a of the firstmotor 116, 216, 316 and the motor casing 116 b, 216 b, 316 b, whereinthe set relative rotational position of the scan arm 103, 203, 303 andthe first suspension arm 109, 209, 309 is sensed. Hence, the fourthposition sensing device comprises a third rotary position encoder 171,271, 371.

A fifth position sensing device 172, 272, 372 is adapted to sense therelative rotational position of a rotor 126 a, 226 a, 326 a of thesecond motor 126, 226, 326 and the motor casing 126 b, 226 b, 326 b,wherein the set relative rotational position of second suspension arm110, 210, 310 and lower portion 111, 211, 311 is sensed. Hence, thefifth position sensing device comprises a fourth rotary position encoder172, 272, 372.

A sixth position sensing device 180, 280, 380 is adapted to sense therelative rotational position of a rotor of the third motor 177, 277, 377and the motor casing 177 b, 277 b, 377 b, wherein the set relativelinear position of the first suspension arm 209, 209, 309 and the secondsuspension arm 110, 210, 310 is sensed by first transforming this datawith regard to the screw pitch of the third linear screw 115, 215, 315.Hence, the sixth position sensing device comprises a fifth rotaryposition encoder 180, 280, 380.

A control unit 121, 221, 321 is connected to the motors 116, 216, 316,126, 226, 326, 177, 277, 377 in order to control the motors and therebythe rotational movement of the first 109, 209, 309 and second 110, 210,310 suspension arms, and the scan arm 103, 203, 303, as well as thelength of the first and second suspension arms. By means of thisarrangement, arbitrary movement in two dimensions of the x-ray source104, 204, 304 and the detector 105, 205, 305 is enabled within themechanical restraints of the rotational limits between the scan arm 103,203, 303 and the first suspension arm 109, 209, 309, the varying of thetotal length of the first and second 110, 210, 310 suspension arm, andthe connection between the x-ray source 104, 204, 304 and the detector105, 205, 305 through the scan arm 103, 203, 303. In the embodimentwherein a scan arm 103, 203, 303 is not present, an additional degree offreedom in the relative movement between the x-ray source 104, 204, 304and the detector 105, 205, 305 is present. When the detector 105, 205,305 and x-ray source 104, 204, 304 are connected by a scan arm 103, 203,303, an x-ray beam 122, 222, 322 irradiated from the x-ray source 104,204, 304 is thus set to be directed towards, and irradiate, the detector105, 205, 305. In any embodiment wherein no scan arm 103, 203, 303 ispresent, and the absolute distance between the x-ray source 104, 204,304 and the detector 105, 205, 305 may vary, a control unit 121, 221,321 is adapted to rotate the x-ray source 104, 204, 304 and the detector105, 205, 305 such that radiation from the x-ray source 104, 204, 304 isadapted to be directed towards, and irradiate the detector 105, 205,305.

During the scan movement of the x-ray source 104, 204, 304 and thedetector 105, 205, 305 in relation to an object, the x-ray source 104,204, 304 may thus be moved along a thought, arbitrary first movementpath that is redefined at any instant in time and between differentscans as well as being rotated during this movement. In a similarmanner, the detector 105, 205, 305 may be moved along a thought,arbitrary second movement path that is redefined at any instant in timeand between different scans, as well as being rotated during thismovement. Further, a scan movement may be referred to as the movement ofthe x-ray source 104, 204, 304 and/or the detector 105, 205, 305 along afirst and a second movement path. The scan movement further comprises asubset movement when the irradiated x-rays are actually impinging on anobject 108, 208, 308 wherein an image of the object can bereconstructed. Such movement is hereinafter referred to as a scan of anobject.

The x-ray apparatus 102, 202, 302 further comprises a position sensingarrangement adapted for sensing positions corresponding to the positionsof the x-ray source and the detector and transmitting the positionsignals the positions of the x-ray source and detector. According oneembodiment, the position sensing arrangement is adapted for sensingpositions corresponding to the positions of the x-ray source and thedetector during their movements along the first and second movementpaths respectively.

The position sensing arrangement of the x-ray apparatus comprises any orall of the first position sensing device 173, 273, 373, second positionsensing device 172, 272, 372, third position sensing device 171, 271,371, fourth position sensing device 172, 272, 372, fifth positionsensing device 178, 278, 378, sixth position sensing device 180, 280,380 or a combination thereof. Each of the first to sixth positionsensing devices is adapted to emit signals corresponding to the sensedrelative positions. Further, each of the first to sixth position sensingdevices is connected to a recording device 179, 279, 379, via a secondconnection device 184, 284, 384 wherein the recording device 179, 279,379 is adapted to receive and record said position signals correspondingto the relative positions.

According to another embodiment, any type of position sensing device maybe used for either sensing the actual positions corresponding to thepositions of the x-ray source and the detector or the set positionscorresponding to the positions of the x-ray source and the detector.Such position sensing devices may comprise devices adapted to senserelative rotational positions that need to be transformed into actualpositions, or positions directly sensing the coordinates of the x-raysource and the detector.

During a scan movement, the recording device 179, 279, 379 is adapted torecord signals corresponding to the relative positions of the positionsensing arrangement, i.e. the entire movement may be recorded in saidrecording device, regardless if the movements correspond to a 2D scan ora 3D scan or any other type of scan movement.

Further, during the scan movement, especially during a scan of anobject, readout of data from the detector concerning the amount ofphotons impinging the detector pixels of each detector strip occurs in afrequent manner in order to acquire the necessary amount of data foreach projection angle of the x-ray source and detector in relation tothe object, necessary for the reconstruction of the image. Read out datais transmitted to an image reconstruction device via a first connectiondevice 183, 283, 383, wherein the image reconstruction device isimplementing back projection algorithms, wherein during reconstructionof the tomosynthesis images or other image types the positions of thex-ray source and the detector for every readout by the detector is takeninto account. The image reconstruction device is connected to therecording device via a third connection device 185, 285, 385, whereinsignals from the recording device can be transmitted from the recordingdevice to the image reconstruction device. The recording device or theimage reconstruction device, or any other device in the x-ray apparatusmay be adapted to deduce the actual positions of the x-ray source andthe detector from the signals of the position sensing arrangement whichcorrespond to the sensed relative positions. Hence, either one of therecording device and the image reconstruction device or any other devicein the x-ray apparatus thus comprises information such as e.g. thelength distance between the x-ray source and the detector, the positionof the pivot point of along the scan arm, etc. which is necessary fortransformation of relative position signals into actual positions orcoordinates of the x-ray source and the detector, as well as means fortransforming the relative position signals into the actual positionsignals of the x-ray source and the detector.

By including the actual positions of the x-ray source and the detectorin the tomosynthesis reconstruction process, the detector readout imagescan be optimized in terms of reduced motion blur effects. Dataconcerning the reconstructed tomosynthesis images or other images aresent to a display device 182, 282, 382, wherein the images can bereviewed and analyzed, for instance by an operator of the system inorder to identify for instance abnormalities in a breast or other partsof the human body.

According to one embodiment, each of the first, second and thirdconnection devices is one of a signal cable or a transmitter forwireless communication.

According to one embodiment, readout of data is performed upon theposition signals from at least one of the fourth, fifth or sixthposition sensors related to the positions of the motors, correspondingto predefined positions for instance defined in the control unit 121,221, 321 for controlling the movement of the motors. The scan movementis recorded by the recording device by recording signals from theposition sensing arrangement.

According to one embodiment, readout of data from the detector isperformed at certain predefined points in time.

According to one embodiment, readout of data is performed upon theposition signals of at least one of the first, second, and thirdposition sensing devices, related to for instance the relative positionsof the scan arm, the first and second suspension arms, the relativeposition of the second suspension arm and a lower portion of the x-rayapparatus, corresponding to predefined positions. The scan movement isrecorded by the recording device by recording signals from the positionsensing arrangement.

Whenever the signals from the third, fourth or sixth position sensingdevice of the position sensing arrangement is recorded by the recordingdevice for recording the scan movement, an alteration or transformationof the signals needs to be performed before the image reconstructionstep in order to take into account the play that may be built into thesystem that causes motion blur. Hence, with knowledge of the exactpositions that corresponds to a certain motor position, i.e. thebuilt-in play in the system for such motor positions, the data can beadjusted before the image reconstruction step. Such information may beretrieved by a system such as the herein described, through acalibration step at the assembly line during production of theapparatus, wherein the exact position signals are recorded from at leastone of the first, second and third position sensing devices parallel tothe recording signals from the fourth, fifth and sixth position sensingdevices of the motors. In this manner, a calibration tool may begenerated wherein exact positions related to every motor position aresaved into the system in a memory device for instance comprised in therecording device or the image reconstruction device.

According to one embodiment, the method comprises the following steps:

1. Start X-ray source, start a scan motion,2. Repeat until exposure stops:

wait until one position encoder reaches a target position, as defined ina table,

readout X-ray detector and store value, and simultaneously readout allother position encoders and store values

lookup next target position, using said table.

3. Exposure off, stop scan motion4. Apply gray-level correction of all data, determine number of slicesto reconstruct and at what coordinates5. For each voxel position, in the volume to reconstruct, determinecorresponding coordinate in the stored detector signals. (Anoptimization, it may be enough to store coordinates along the scandirection)The coordinates are determined by mapping a straight line from the X-raysource position, through the voxel's location in real world space, andtowards unto a projection images. This operation involves geometryaccording to any person skilled in the art of geometry, wherein theX-ray source position is calculated by looking up the correspondingrecorded positions, and calculating a coordinate in the projection imagedata, based on a samples of recorded data. This lookup involvescomputing an inverse of a sampled function. Methods may be iterativegradient descent/inverse interpolation.(Geometric calculations involves dimensions of mechanical parts in theapparatus, some of which may be pre-calibrated by scanning a knownobject with a set of sharp edges.)6. Preferably, we also compute inverse of the local coordinatetransformations, i.e. compute each projection image pixel's coordinatesin the voxel to reconstruct.7. Reconstruct image, using back projection, or preferably iterativereconstruction algorithm, involving back projection and its inverse, andback projection again, etc. This step relies on resampling projectionimages, or filtered/processed versions thereof, wherein the resamplinguses the computed coordinate transformations8. Display image or a slice thereof, or send the image volume to anarchive, commonly known as PACS.

1. An x-ray apparatus comprising: an x-ray source adapted to emit anx-ray beam, a detector adapted to receive the x-ray beam of the x-raysource, wherein the x-ray source is adapted to be moved in relation to afirst portion of the x-ray apparatus, wherein the detector is adapted tobe moved in relation to a first portion of the x-ray apparatus, thex-ray apparatus further comprising a control unit for controlling themovement of the x-ray source and detector, wherein the x-ray source andthe detector are adapted to rotate in relation to a first portion of thex-ray apparatus, wherein further the x-ray beam is directed essentiallytowards the detector during the movement of the x-ray source and thedetector, wherein the control unit is adapted to receive external data,wherein the control unit is further adapted to control the movement ofthe x-ray source and the detector based on external data, wherein thex-ray apparatus further comprises at least one position adjustablecompression paddle, and a means for determining the position of the atleast one compression paddle adapted to output paddle position datacorresponding to the position of the at least one compression paddle,and wherein the external data, which is received by the control unit,comprises paddle position data, wherein the control unit is adapted tocontrol a scan movement and/or the remainder of a scan movement of thex-ray source and the detector based on the external data, such that atomosynthetic scan movement is performed, wherein tomographic projectionangles of an object placed in the x-ray beam are optimized based on theexternal data.
 2. An x-ray apparatus according to claim 1, wherein thedetector is adapted to sense characteristics of an x-ray beam in realtime during a scan movement, wherein the detector is further adapted tooutput x-ray beam data corresponding to characteristics of the x-raybeam, and wherein the external data, which is received by the controlunit for controlling the remainder of the scan movement of the x-raysource and the detector, comprises x-ray beam data.
 3. An x-rayapparatus according to claim 1, wherein the detector is adapted toreceive impinging photons from the x-ray source during a scan movement,the detector further being adapted to detect an x-ray intensity based onthe rate of impinging photons, wherein the control unit is furtheradapted to receive external data from the detector that a scan of anobject placed in the x-ray beam is initiated by detecting a lowerintensity, as an object to be scanned starts attenuating photons fromthe x-ray beam.
 4. An x-ray apparatus according to claim 3, wherein thecontrol unit is adapted to control the movement of x-ray source and thedetector such that the speed of at least the x-ray source decreases asthe first end of the detector senses a decreased count rate at leastduring the scan of the object.
 5. An x-ray apparatus according to claim3, wherein a first detected x-ray intensity decreases the speed of atleast the x-ray source to a first velocity, a second detected x-rayintensity decreases the speed of the x-ray source to a second velocity,wherein, if the first detected x-ray intensity is lower than the seconddetected x-ray intensity, the first velocity is lower than the secondvelocity at least during a scan of the object.
 6. An x-ray apparatusaccording to claim 1, wherein the control unit is adapted to control thespeed of the detector such that the velocity of the detector is lowerthan the speed of the x-ray source at least during a scan of an object.7. An x-ray apparatus according to claim 5, wherein the control unit isadapted to control the speed of the x-ray source and the detector suchthat a ratio between the velocity of the x-ray source and the detectoris lower for a lower lower detected x-ray intensity compared to a higherdetected x-ray intensity during a scan of the object and/or comparedbetween two separate scan of objects.
 8. An x-ray apparatus according toclaim 6, wherein the control unit is adapted to control the speed of thex-ray source and the detector such that the ratio is high enough toallow the x-ray source to pass the detector in a horizontal directionduring the movement of the x-ray source and the detector, wherein thecount rate corresponds to the object being scanned.
 9. An x-rayapparatus according to claim 1, wherein the control unit is adapted tocontrol the speed of at least the x-ray source based on the position ofthe at least one compression paddle during a scan of the object suchthat a first position of the at least one compression paddle sets thespeed of at least the x-ray source to a first velocity, a secondposition of the at least one compression paddle sets the speed of atleast the x-ray source to a second velocity, wherein, if the firstposition of the at least one compression paddle is higher in a verticaldirection than the second position of the at least one compressionpaddle, the first velocity is lower than the second velocity.
 10. Anx-ray apparatus according to claim 9, wherein the control unit isadapted to control the speed of the x-ray source and the detector suchthat a ratio between the velocity of the x-ray source and the detectoris lower for a higher position of the compression paddle compared to alower position of the compression paddle at least during a scan of theobject.
 11. An x-ray apparatus according to claim 9, wherein the controlunit is adapted to control the speed of the x-ray source and thedetector such that the ratio is high enough to allow the x-ray source topass the detector in a horizontal direction at least during a scan ofthe object.
 12. An x-ray apparatus according to claim 3, wherein thecontrol unit is adapted to control the movement of the x-ray source andthe detector such that a straight line between the x-ray source and acentre of the detector in relation to a vertical line essentiallyextending through a first portion of the x-ray apparatus defines anangle (α) wherein the detector moves before the x-ray source towards theobject to be scanned, wherein the angle (α) is set during a start of amovement of the x-ray source and the detector until scan of an object isinitiated, wherein the angle (α) decreases with the position of the atleast one compression paddle.
 13. An x-ray apparatus according to claim12 wherein the control unit is adapted to control the speed of the x-raysource and the detector such that the ratio there between is high enoughso that the angle (α) has a first value, passes 0 degrees and has asecond value at the end of the scan of an object, wherein the first andsecond values essentially maximized under constraint of avoidingcollision with a compression paddle.
 14. An x-ray apparatus according toclaim 12, wherein the control unit is adapted to control the angle (α)such that the spread of local tomographic projection angles remainsconstant during the entire scan movement.
 15. An x-ray apparatusaccording to claim 12, wherein the control unit is adapted to controlthe movement of the x-ray source and the detector such that the angle(α) does not exceed a limit value, wherein the limit value iscontinuously varying with the position of the x-ray source and thepositions of the detector, and furthermore depends on the position andtype of the compression paddle.
 16. An x-ray apparatus according toclaim 16, wherein the limit value of angle (α) depends on the positionof the at least one compression paddle.
 17. An x-ray apparatus accordingto claim 15, wherein the apparatus comprises two compression paddles,wherein an object can be compressed between said two compressionpaddles, wherein the limit value of angle (α) decreases if the distancebetween the compression paddles increases.
 18. An x-ray apparatusaccording to claim 1, further comprising a scan arm, wherein the x-raysource is arranged at a first position on the scan arm and the detectoris arranged at a second position on the scan arm.
 19. An x-ray apparatusaccording to claim 18, wherein the first position of the scan armcorresponds to a first end of the scan arm and the second position ofthe scan arm corresponds to a second end of the scan arm.
 20. An x-rayapparatus according to claim 18, wherein the scan arm further comprisesa multi-slit collimator arranged between the x-ray source and thedetector on the scan arm, wherein the control unit is adapted to controlthe movement of the x-ray source and the detector such that a collisionbetween the at least on compression paddle and the collimator isprevented.
 21. An x-ray apparatus according to claim 1, wherein thecontrol unit is adapted to change direction of the x-ray source and/orthe detector at a first turning point for the x-ray source and at afirst turning point for the detector respectively, wherein the x-raysource either moves in a second direction or stops after reaching thefirst turning point and the detector either moves in a second directionor stops after reaching the first turning point, and wherein the seconddirections are essentially opposite the first directions before reachingthe first turning points.
 22. An x-ray apparatus according to claim 21,wherein the control unit is further adapted to select the number ofturning points, zero or more, and their positions depending on saidexternal data.
 23. An x-ray apparatus according to claim 21, wherein thecontrol unit is further adapted to minimize the number of turning pointsunder the constraint of achieving tomo-angles in the object scan,depending on said external data.
 24. An x-ray apparatus according toclaim 21, wherein the control unit is adapted to control the movement ofthe x-ray source and the detector such that when both the x-ray sourceand the detector move towards their first turning points the x-raysource reaches the first turning point before the detector reaches thefirst turning point.
 25. An x-ray apparatus according to claim 24,wherein the control unit is adapted to control the movement of the x-raysource and the detector such that the x-ray source and the detectorchanges direction immediately after reaching the first turning point andstarts to move in a second direction.
 26. An x-ray apparatus accordingto claim 24, wherein the control unit is adapted to change direction ofthe x-ray source at a second turning point, wherein the control unit isadapted to control the movement of the x-ray source and the detectorsuch that the x-ray source changes direction and starts to move in afirst direction at the second turning point when the detector reachesthe first turning point.
 27. An x-ray apparatus according to claim 22,wherein the x-ray stops after reaching the first turning point until theother of the x-ray source and detector reaches the first turning point,whereafter the x-ray source or starts to move in a second direction. 28.An x-ray apparatus according to claim 24, wherein the x-ray source moveswith a higher speed than the detector.
 29. An x-ray apparatus accordingto claim 1 wherein the control unit is further adapted to control themovement of the x-ray source and the detector based on a positions ofthe x-ray source and the detector.
 30. An x-ray apparatus according toclaim 29, wherein the positions are predefined.
 31. An x-ray apparatusaccording to claim 30 wherein the control unit is adapted to control themovement of the x-ray source and the detector such that the speed of thex-ray source is higher than the speed of the detector.
 32. An x-rayapparatus according to claim 28, wherein the predefined positionscorresponds to positions reached during a scan of an object, whereby anarea in the object has been identified that requires a specific scanmovement, wherein the ratio of the speed of the x-ray source and thedetector increases.
 33. An x-ray apparatus according to claim 1, whereinan optimization is performed for maximizing a tomographic angle within adetected object, under a tradeoff of minimizing the movement of theX-ray source.
 34. An x-ray apparatus according to claim 30, wherein thatthe speed of at least the x-ray source decreases as the predefinedposition of the x-ray source is reached, and the predefined position ofthe detector is reached.
 35. An x-ray apparatus according to claim 34,wherein the x-ray apparatus further comprises a device for taking biopsysamples from a breast as the positions are reached, wherein thepositions corresponds to positions whereby an area in the object isidentified that requires biopsy sampling.
 36. An x-ray apparatusaccording to claim 1, wherein the x-ray apparatus comprises an upperportion and a lower portion, wherein the x-ray source is pivotallyarranged in a first end of a first suspension arm, wherein the secondend of a first suspension arm being slidingly arranged in a first end ofa second suspension arm, wherein a second end of the second suspensionarm is pivotally arranged in a lower portion, wherein a first linearscrew is arranged in the x-ray portion near the x-ray source to controlthe movement of the x-ray source in a horizontal direction, a secondlinear screw is arranged in the lower portion near the detector assemblyto control the movement of the detector assembly in a horizontaldirection, and a third linear screw is arranged in the second suspensionarm to control the movement of the scan arm in a vertical direction. 37.An x-ray apparatus according to claim 1, wherein the first portion ofthe x-ray apparatus is essentially fixed in space.
 38. An x-rayapparatus comprising: an x-ray source adapted to emit an x-ray beam, adetector adapted to receive the x-ray beam of the x-ray source, whereinthe x-ray source is set up to be moved, wherein the detector is set upto be moved, the x-ray apparatus further comprising a control unit forcontrolling the movement of the x-ray source and detector, whereinfurther the x-ray beam is directed essentially towards the detectorduring the movement of the x-ray source and the detector, wherein thecontrol unit is adapted receive external data, wherein the to controlunit is further adapted to control the path of movement of thecombination of the x-ray source and the detector based on said externaldata wherein external data comprises data related to an object.
 39. Anx-ray apparatus according to claim 1, wherein the control unit isadapted to control the movement of the x-ray source along a firstmovement path and control the movement of the detector along a secondmovement path respectively during a scan movement, based on externaldata.
 40. An x-ray apparatus according to claim 1, wherein the externaldata is received by the control unit during the scan movement.
 41. Anx-ray apparatus according to claim 1, wherein the external data isrelated to a boundary or thickness of an object to be scanned, or aregion of interest, wherein said apparatus comprises means for measuringsaid external data after positioning the object but before finishing ascan.
 42. An x-ray apparatus according to claim 39, wherein movement ofthe x-ray source along a first movement path and the movement of thedetector along the second movement path, corresponds to a combinedmovement path, wherein said combined movement path can be represented bya curve through a multi-dimensional parametric space involving aposition along one axis and an angle between said x-ray source anddetector.
 43. An x-ray apparatus according to claim 1, wherein saidfirst movement path and said second movement path is adapted foroptimizing local tomographic projection angles and minimizing movementsof said x-ray source.